WARRANT TO PURCHASE STOCK

Exhibit 4.2

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS, OR PURSUANT TO RULE 144 OR AN EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS.

THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A LOCK-UP PERIOD OF UP TO 180 DAYS FOLLOWING THE EFFECTIVE DATE OF A REGISTRATION STATEMENT OF THE COMPANY FILED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, SUBSTANTIALLY AS SET FORTH IN A WARRANT TO PURCHASE STOCK BETWEEN THE COMPANY AND THE HOLDER, A COPY OF WHICH MAY BE OBTAINED AT THE COMPANY’S PRINCIPAL OFFICE. SUCH LOCK-UP PERIOD IS BINDING ON TRANSFEREES OF THESE SECURITIES.

WARRANT TO PURCHASE STOCK

THIS WARRANT TO PURCHASE STOCK (“WARRANT”) CERTIFIES THAT, for good and valuable consideration, the receipt of which is hereby acknowledged, COMERICA BANK, or its assignee (“Holder”), is entitled to purchase the number of fully paid and nonassessable shares of the class of securities (the “Shares”) of MAVENIR SYSTEMS, INC. (the “Company”) at the initial exercise price per Share (the “Warrant Price”) all as set forth above and as adjusted pursuant to this Warrant, subject to the provisions and upon the terms and conditions set forth in this Warrant. The definition of “Shares”, the Warrant Price and the number of Shares issuable upon exercise of this Warrant are subject to adjustment in accordance with Section 2.1 in the event of a Qualified Financing (as defined below).

ARTICLE 1

EXERCISE

1.1 Method of Exercise. Holder may exercise this Warrant by delivering this Warrant and a duly executed Notice of Exercise in substantially the form attached as Appendix 1 to the principal office of the Company. Holder shall also deliver to the Company a check or wire for the aggregate Warrant Price for the Shares being purchased.

1.2 Delivery of Certificate and New Warrant. Within 45 days after Holder exercises this Warrant, the Company shall deliver to Holder certificates for the Shares acquired and, if this Warrant has not been fully exercised and has not expired, a new warrant representing the Shares not so acquired.

1.3 Replacement of Warrants . In the case of loss, theft or destruction of this Warrant, on delivery of an indemnity agreement reasonably satisfactory in form and amount to the Company or, in the case of mutilation, on surrender and cancellation of this Warrant, the Company at its expense shall execute and deliver, in lieu of this Warrant, a new warrant of like tenor.

1.4 Acquisition of the Company.

1.4.1 “Acquisition.” For the purpose of this Warrant, “Acquisition” means (a) the acquisition of the Company by another entity by means of any transaction or series of related transactions (including, without limitation, any merger, consolidation or other form of reorganization in which outstanding shares of the Company are exchanged for securities or other consideration issued, or caused to be issued, by the acquiring entity or its subsidiary, but excluding any transaction effected primarily for the purpose of changing the Company’s jurisdiction of incorporation) that results in the transfer or acquisition of at least a majority of the Company’s voting power to such entity, or (b) a sale of all or substantially all of the assets of the Company or the exclusive license of all or substantially all of the Company’s intellectual property by means of any transaction or series of related transactions.

1.4.2 Treatment of Warrant in the Event of an Acquisition. The Company shall give Holder written notice at least 20 days prior to the closing of any proposed Acquisition. The Company will use its commercially reasonable efforts to cause the acquirer of the Company under the Acquisition (the “Acquirer”) to assume this Warrant as a part of the Acquisition.

(A) If the Acquirer assumes this Warrant, then this Warrant shall be exercisable for the same securities, cash, and property as would be payable for the Shares issuable upon exercise of the unexercised portion of this Warrant as if such Shares were outstanding on the record date for the Acquisition and subsequent closing. The Warrant Price shall be adjusted accordingly, and the Warrant Price and number and class of Shares shall continue to be subject to adjustment from time to time in accordance with the provisions hereof.

(B) If the Acquirer refuses to assume this Warrant in connection with the Acquisition, the Company shall give Holder an additional written notice at least 5 days prior to the closing of the Acquisition of such fact. In such event, notwithstanding any other provision of this Warrant to the contrary, Holder may immediately exercise this Warrant in the manner specified in this Warrant with such exercise effective immediately prior to closing of the Acquisition. If Holder elects not to exercise this Warrant, then this Warrant will terminate immediately prior to the closing of the Acquisition.

ARTICLE 2

ADJUSTMENTS TO THE SHARES

2.1 Qualified Financing.

2.1.1 “Qualified Financing.” For the purpose of this Warrant, “Qualified Financing” means the next transaction (or series of related transactions) after the date of this Warrant in which the Company issues and sells shares of its capital stock in exchange for aggregate gross cash proceeds of at least $8.0 million (excluding any amounts received upon conversion of indebtedness).

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2.1.2 Adjustment in the Event of a Qualified Financing. Notwithstanding anything in this Warrant to the contrary, in the event that the Company issues equity securities in a Qualified Financing prior to January 15, 2009, this Warrant shall be exercisable for the number of equity securities issued in such Qualified Financing equal to the quotient obtained by dividing (x) by (y), where (x) is an amount equal to $75,000 and (y) is equal to the price per share at which the Company sells the equity securities issued in a Qualified Financing. In the event of such adjustment, the Warrant Price shall be equal to the price per share paid for the equity securities issued in such Qualified Financing.

2.2 Stock Dividends, Splits, Etc. If the Company subdivides the outstanding Shares, then upon exercise of this Warrant, for each Share acquired, Holder shall receive, without cost to Holder, the total number and kind of securities to which Holder would have been entitled had Holder owned the Shares of record as of the date the dividend or subdivision occurred.

2.3 Reclassification, Exchange or Substitution. Upon any reclassification, exchange, substitution, or other event that results in a change of the number and/or class of the securities issuable upon exercise or conversion of this Warrant, Holder shall be entitled to receive, upon exercise or conversion of this Warrant, the number and kind of securities and property that Holder would have received for the Shares if this Warrant had been exercised immediately before such reclassification, exchange, substitution, or other event. Such an event shall include any automatic conversion of the outstanding or issuable securities of the Company of the same class or series as the Shares to common stock pursuant to the terms of the Company’s Certificate of Incorporation upon the closing of a registered public offering of the Company’s common stock. The Company or its successor shall promptly issue to Holder a new warrant for such new securities or other property. The new warrant shall provide for adjustments which shall be as nearly equivalent as may be practicable to the adjustments provided for in this Article 2 including, without limitation, adjustments to the Warrant Price and to the number of securities or property issuable upon exercise of the new warrant. The provisions of this Section 2.3 shall similarly apply to successive reclassifications, exchanges, substitutions, or other events.

2.4 Adjustments for Combinations, Etc. If the outstanding Shares are combined or consolidated, by reclassification, reverse split or otherwise, into a lesser Number of Shares, the Warrant Price shall be proportionately increased. If the outstanding Shares are split or multiplied, by reclassification or otherwise, into a greater Number of Shares, the Warrant Price shall be proportionately decreased.

2.5 Adjustments for Diluting Issuances. The Shares issuable upon exercise of this Warrant are subject to the anti-dilution protection set forth in the Company’s Amended and Restated Certificate of Incorporation as in effect on the Issue Date and as amended from time to time thereafter; provided, however, that under no circumstances shall the aggregate Warrant Price payable by the Holder upon exercise of this Warrant increase as a result of any adjustment arising from the issuance, after the Issue Date, of securities at a price per share less than the Warrant Price.

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2.6 No Impairment. The Company shall not, by amendment of its Certificate of Incorporation or through a reorganization, transfer of assets, consolidation, merger, dissolution, issue, or sale of securities or any other voluntary action, avoid or seek to avoid the observance or performance of any of the terms to be observed or performed under this Warrant by the Company, but shall at all times in good faith assist in carrying out all the provisions of this Article 2 and in taking all such action as may be necessary or appropriate to protect Holder’s rights under this Article 2 against impairment.

2.7 Certificate as to Adjustments. Upon each adjustment of the Warrant Price, the Company at its expense shall promptly compute such adjustment, and furnish Holder with a certificate signed by its Chief Financial Officer setting forth such adjustment and the facts upon which such adjustment is based. The Company shall, upon written request, furnish Holder a certificate setting forth the Warrant Price in effect upon the date thereof and the series of adjustments leading to such Warrant Price.

2.8 Fractional Shares. No fractional Shares shall be issuable upon exercise of this Warrant and the Number of Shares to be issued shall be rounded down to the nearest whole Share. If a fractional share interest arises upon any exercise of the Warrant, the Company shall eliminate such fractional share interest by paying Holder an amount computed by multiplying the fractional interest by the fair market value, as determined by the Company’s Board of Directors, of a full Share.

ARTICLE 3

REPRESENTATIONS AND COVENANTS OF THE COMPANY

3.1 Representations and Warranties. The Company hereby represents and warrants to, and agrees with, the Holder as follows:

3.1.1 The initial Warrant Price referenced on the first page of this Warrant is not greater than the price per share last paid by holders of Series B Preferred Stock.

3.1.2 All Shares which may be issued upon the exercise of the purchase right represented by this Warrant, and all securities, if any, issuable upon conversion of the Shares, shall, upon issuance, be duly authorized, validly issued, fully paid and nonassessable, and free of any liens and encumbrances except for restrictions on transfer provided for herein or under applicable federal and state securities laws.

3.1.3 The Company’s capitalization table attached to this Warrant is true and complete as of the Issue Date.

3.2 Notice of Certain Events. If the Company proposes at any time (a) to declare any dividend or distribution upon its stock, whether in cash, property, stock, or other securities and whether or not a regular cash dividend; (b) to offer for subscription pro rata to the holders of any class or series of its stock any additional shares of stock of any class or series or other rights; (c) to effect any reclassification or recapitalization of stock; or (d) to merge or consolidate with or into any other corporation, or sell, lease, license, or convey all or substantially all of its assets, or to liquidate, dissolve or wind up, then, in connection with each such event, the Company shall give Holder (1) at least 15 days prior written notice of the date on which a record will be taken for such dividend, distribution, or subscription rights (and specifying the date on which the holders of stock will be entitled thereto) or for determining rights to

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vote, if any, in respect of the matters referred to in (a) and (b) above; and (2) in the case of the matters referred to in (c) and (d) above at least 15 days prior written notice of the date when the same will take place (and specifying the date on which the holders of stock will be entitled to exchange their stock for securities or other property deliverable upon the occurrence of such event).

3.3 Information Rights. So long as the Holder holds this Warrant and/or any of the Shares, the Company shall deliver to the Holder (a) promptly after mailing, copies of all communiqués to the shareholders of the Company, (b) within one hundred fifty (150) days after the end of each fiscal year of the Company, the annual audited financial statements of the Company certified by independent public accountants of recognized standing and (c) within thirty (30) days after the end of each of each month, the Company’s monthly, unaudited financial statements.

3.4 Registration Under Securities Act of 1933, as amended. The Company agrees that the Shares or, if the Shares are convertible into common stock of the Company, such common stock, shall be subject to the registration rights set forth on Exhibit A.

3.5 Investment Representations of the Holder. With respect to the acquisition of any of the Shares, the Holder hereby represents and warrants to the Company as follows:

3.5.1 Purchase Entirely for Own Account. This Warrant is made with the Holder in reliance upon the Holder’s representation to the Company, which by the Holder’s execution of this Warrant the Holder hereby confirms, that the Shares will be acquired for investment for the Holder’s own account, not as a nominee or agent, and not with a view to the resale or distribution of any part thereof, and that the Holder has no present intention of selling, granting any participation in, or otherwise distributing the same. By executing this Warrant, the Holder further represents that the Holder does not have any contract, undertaking, agreement or arrangement with any person to sell, transfer or grant participations to such person or to any third person with respect to any of the Shares.

3.5.2 Reliance upon Holders’ Representations. The Holder understands that the Shares have not been, and will not be, registered under the Securities Act of 1933, as amended (the “Securities Act”) by reason of a specific exemption from the registration provisions of the Securities Act, and that the Company’s reliance on such exemption is predicated on the Holder’s representations set forth herein.

3.5.3 Investment Experience; Economic Risk. The Holder understands that the Company has a limited financial and operating history and that an investment in the Company involves substantial risks. The Holder is experienced in evaluating and investing in private placement transactions of securities of companies in a similar stage of development to that of the Company and acknowledges that the Holder is able to fend for itself. The Holder has such knowledge and experience in financial and business matters that the Holder is capable of evaluating the merits and risks of the investment in the Shares. The Holder can bear the economic risk of the Holder’s investment and is able, without impairing the Holder’s financial condition, to hold the Shares for an indefinite period of time and to suffer a complete loss of the Holder’s investment.

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3.5.4 Accredited Investor Status. The Holder is an “accredited investor” within the meaning of Regulation D, Rule 501(a), promulgated under the Securities Act. The Holder also represents that it has not been organized for the purpose of acquiring the Shares.

3.5.5 Restricted Securities. The Holder understands that the Shares are characterized as “restricted securities” under the federal securities laws inasmuch as they are being acquired from the Company in a transaction not involving a public offering and that under such federal securities laws and applicable regulations such Shares may be resold without registration under the Securities Act only in certain limited circumstances. In this connection, Holder represents that it is aware of the provisions of Rule 144 promulgated under the Securities Act which permit limited resale of securities purchased in a private placement subject to the satisfaction of certain conditions, including, among other things, the existence of a public market for the securities and the availability of certain current public information about the Company.

3.5.6 Market Standoff. The Holder hereby agrees that, if requested by the managing underwriter, it will not, without the prior written consent of the Company, during the period commencing on the date of the final prospectus relating to the Company’s initial public offering or any secondary public offering, as applicable, and ending on the date specified by the Company and the managing underwriter (such period not to exceed one hundred eighty (180) calendar days in the case of an initial public offering and ninety (90) calendar days in the case of any secondary public offering (or such other period as may be requested by the Company or managing underwriter to accommodate regulatory restrictions on (a) the publication or other distribution of research reports and (b) analyst recommendations and opinions, including, but not limited to, the restrictions contained in NASD Rule 2711(f)(4) or NYSE Rule 472(f)(4), or any successor provisions or amendments thereto)) (i) lend, offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any securities of the Company, including (without limitation) shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock (whether now owned or hereafter acquired) or (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of any securities of the Company, including (without limitation) shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock (whether now owned or hereafter acquired), whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of securities, in cash or otherwise. The foregoing covenants shall not apply to the sale of any shares by the Holder to an underwriter pursuant to an underwriting agreement and shall only be applicable to the Holder if all the Company’s executive officers, directors and greater than one percent (1%) stockholders enter into similar agreements. The Holder agrees to execute an agreement(s) reflecting (i) and (ii) above as may be requested by the managing underwriters at the time of the initial public offering or any secondary public offering, and further agrees that the Company may impose stop transfer instructions with its transfer agent in order to enforce the covenants in (i) and (ii) above. The restrictions in this Section 3.5.6 shall not apply to transfers to affiliates of the Holder or purchases made in the open market following the completion of any offering covered by this Section 3.5.6 or to any resale public offerings in which the Holder is not selling shares of Common Stock for its own account.

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ARTICLE 4

MISCELLANEOUS

4.1 Term; Exercise Upon Expiration. This Warrant is exercisable in whole or in part, at any time and from time to time on or before the Expiration Date set forth above; provided, however, that if the Company completes its initial public offering within the one-year period immediately prior to the Expiration Date, the Expiration Date shall automatically be extended until the first anniversary of the effective date of the Company’s initial public offering.

4.2 Legends. This Warrant and the Shares (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) shall be imprinted with a legend in substantially the following form:

THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS, OR PURSUANT TO RULE 144 OR OPINION OF COUNSEL OR OTHER EVIDENCE, REASONABLY SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT THERE EXISTS A VALID AND APPLICABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS.

THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A LOCK-UP PERIOD OF UP TO 180 DAYS FOLLOWING THE EFFECTIVE DATE OF A REGISTRATION STATEMENT OF THE COMPANY FILED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, SUBSTANTIALLY AS SET FORTH IN A WARRANT TO PURCHASE STOCK BETWEEN THE COMPANY AND THE HOLDER, A COPY OF WHICH MAY BE OBTAINED AT THE COMPANY’S PRINCIPAL OFFICE. SUCH LOCK-UP PERIOD IS BINDING ON TRANSFEREES OF THESE SECURITIES.

4.3 Compliance with Securities Laws on Transfer. This Warrant and the Shares issuable upon exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) may not be transferred or assigned in whole or in part without compliance with applicable federal and state securities laws by the transferor and the transferee.

4.4 Transfer Procedure. Subject to the provisions of Section 4.3, Holder may transfer all or part of this Warrant or the Shares issuable upon exercise of this Warrant (or the securities issuable, directly or indirectly, upon conversion of the Shares, if any) by giving the Company written notice of the portion of this Warrant being transferred setting forth the name, address and taxpayer identification number of the transferee and surrendering this Warrant to the Company for reissuance to the transferee(s) (and Holder, if applicable); provided, however, that Holder may transfer all or part of this Warrant to its affiliates, including, without limitation, Comerica Incorporated, at any time without notice or the delivery of any other instrument to the Company, and such affiliate shall then be entitled to all the rights of Holder under this Warrant and any related agreements, and the Company shall cooperate fully in ensuring that any stock issued upon exercise of this Warrant is issued in the name of the affiliate that exercises this Warrant. The terms and conditions of this Warrant shall inure to the benefit of, and be binding upon, the Company and the holders

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hereof and their respective permitted successors and assigns. Unless the Company is filing financial information with the SEC pursuant to the Securities Exchange Act of 1934, the Company shall have the right to refuse to transfer any portion of this Warrant to any person who directly competes with the Company.

4.5 Notices. All notices and other communications from the Company to the Holder, or vice versa, shall be deemed delivered and effective when given personally or mailed by first-class registered or certified mail, postage prepaid, at such address as may have been furnished to the Company or the Holder, as the case may be, in writing by the Company or such Holder from time to time. All notices to the Holder shall be addressed as follows:

Comerica Bank c/o Comerica Incorporated

Attn: Warrant Administrator

500 Woodward Avenue, 32^nd Floor, MC 3379

Detroit, MI 48226

All notices to the Company shall be addressed as follows:

Mavenir Systems, Inc.

Attn: Chief Financial Officer

1651 North Glenville Drive, Suite 201

Richardson, TX 75081

4.6 Amendments. This Warrant and any term hereof may be changed, waived, discharged or terminated only by an instrument in writing signed by the party against which enforcement of such change, waiver, discharge or termination is sought.

4.7 Attorneys’ Fees. In the event of any dispute between the parties concerning the terms and provisions of this Warrant, the party prevailing in such dispute shall be entitled to collect from the other party all costs incurred in such dispute, including reasonable attorneys’ fees.

4.8 Governing Law. This Warrant shall be governed by and construed in accordance with the laws of the State of Delaware, without giving effect to its principles regarding conflicts of law.

4.9 Confidentiality. The Company hereby agrees to keep the terms and conditions of this Warrant confidential. Notwithstanding the foregoing confidentiality obligation, the Company may disclose information relating to this Warrant as required by law, rule, regulation, court order or other legal authority, provided that (i) the Company has given Holder at least ten (10) days’ notice of such required disclosure, and (ii) the Company only discloses information that is required, upon the advice of counsel, to be disclosed.

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APPENDIX 1

NOTICE OF EXERCISE

1. The undersigned hereby elects to purchase                      shares of the                      stock of Mavenir Systems, Inc. pursuant to the terms of the attached Warrant, and tenders herewith payment of the purchase price of such shares in full.

2. Please issue a certificate or certificates representing said shares in the name of the undersigned or in such other name as is specified below:

Comerica Bank

Attn: Warrant Administrator

500 Woodward Avenue, 32^nd Floor, MC 3379

Detroit, MI 48226

3. The undersigned represents it is acquiring the shares solely for its own account and not as a nominee for any other party and not with a view toward the resale or distribution thereof except in compliance with applicable securities laws and hereby makes the representations and warranties set forth in Section 3.5 of the attached Warrant.

COMERICA BANK or Assignee

EXHIBIT A

Registration Rights

The Shares (if common stock), or the common stock issuable upon conversion of the Shares, shall be deemed “registrable securities” for the purpose of being entitled to “piggy back” registration rights in accordance with the terms of the following agreement (the “Agreement”) between the Company and its investor(s):

Amended and Restated Investor’s Rights Agreement dated January 29, 2008, by and among the Company, the Investors listed on Schedule A attached thereto and the Common Holders listed on Schedule B attached thereto, as amended from time to time hereafter.

The Company agrees that no amendments will be made to the Agreement which would have an adverse impact on Holder’s registration rights thereunder without the consent of Holder unless such amendment affects all other holders of equivalent registration rights in the same manner. By acceptance of the Warrant to which this Exhibit A is attached, Holder shall be deemed to be a party to the Agreement solely for the purpose of the above-mentioned registration rights and shall be subject to all restrictions as set forth therein.