Additional Proxy Soliciting Materials (Form DEFA14A)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

CSG SYSTEMS INTERNATIONAL, INC.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

The following was sent by an authorized representative of CSG Systems International, Inc., a Delaware corporation, to all of its employees

NEC Acquisition Update

This message is being sent to all CSG employees.

Dear Fellow CSGers,

We want to keep you updated on the announced transaction with NEC as it progresses towards closing. Over the past several weeks, the parties have hit several important milestones:

On behalf of the entire CSG leadership team, thank you for continuing to elevate our culture and build momentum for a strong 2025 finish and a good start to 2026.

Wishing all of you a very happy holiday season.

Rasmani

FORWARD-LOOKING STATEMENTS

The foregoing contains "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. Forward-looking statements include, but are not limited to, statements concerning the Company's expectations, plans, intentions, strategies or prospects with respect to the proposed transaction. These statements are often identified by the use of words such as "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "plan," "hope," "hopeful," "likely," "may," "optimistic," "possible," "potential," "preliminary," "project," "should," "will," "would" or the negative or plural of these words or similar expressions or variations. Forward-looking statements are made based upon management's current expectations and beliefs and are not guarantees of future performance. Such forward-looking statements are subject to a number of risks, uncertainties, assumptions and other factors that could cause actual results and the timing of certain events to differ materially from future results expressed or implied by the forward-looking statements. These factors include, among others: (i) the ability of the parties to complete the proposed transaction on the anticipated terms and timing, or at all, (ii) the satisfaction or waiver of other conditions to the completion of the proposed transaction, including obtaining required shareholder and regulatory approvals; (iii) the risk that the Company's stock price may fluctuate during the pendency of the proposed transaction and may decline if the proposed transaction is not completed; (iv) potential litigation relating to the proposed transaction that could be instituted against the Company or its directors, managers or officers, including the delay, expense or other effects of any outcomes related thereto; (v) the risk that disruptions from the proposed transaction will harm the Company's business, including current plans and operations, including during the pendency of the proposed transaction; (vi) the ability of the Company to retain, motivate and hire key personnel; (vii) the diversion of management's time and attention from ordinary course business operations to completion of the proposed transaction and integration matters; (viii) potential adverse reactions or changes to business relationships resulting from the pendency or completion of the proposed transaction; (ix) legislative, regulatory and economic developments; (x) potential business uncertainty, including changes to existing business relationships, during the pendency of the proposed transaction that could affect the Company's financial performance; (xi) certain restrictions during the pendency of the proposed transaction that may impact the Company's

ability to pursue certain business opportunities or strategic transactions; (xii) unpredictability and severity of catastrophic events, including but not limited to acts of terrorism, outbreaks of war or hostilities or global pandemics, as well as management's response to any of the aforementioned factors; (xiii) the possibility that the proposed transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events; (xiv) unexpected costs, liabilities or delays associated with the transaction; (xv) the response of competitors to the transaction; (xvi) the occurrence of any event, change or other circumstance that could give rise to the termination of the proposed transaction, including in circumstances requiring the Company to pay a termination fee; (xvii) the ability to realize the anticipated benefits of the proposed transaction, including the expected synergies and cost saving; (xviii) the possibility that competing or superior acquisition proposals for the Company will be made; and (xix) other risks set forth under the heading "Risk Factors," of the Company's Annual Report on Form 10-K for the year ended December 31, 2024 and in the Company's subsequent filings with the Securities and Exchange Commission. You should not rely upon forward-looking statements as predictions of future events. Furthermore, such forward-looking statements speak only as of the date of this report. Actual results could differ materially from the results described in or implied by such forward-looking statements. Forward-looking statements speak only as of the date hereof, and, except as required by law, the Company undertakes no obligation to update or revise these forward-looking statements.

ADDITIONAL INFORMATION AND WHERE TO FIND IT

This communication does not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities or a solicitation of any vote or approval. This communication relates to a proposed acquisition of CSG Systems International, Inc. by NEC Corporation. In connection with this proposed acquisition, CSG Systems International, Inc. may file one or more proxy statements or other documents with the SEC. This communication is not a substitute for any proxy statement or other document that CSG Systems International, Inc. has filed or may file with the SEC in connection with the proposed transaction. INVESTORS AND SECURITY HOLDERS OF CSG SYSTEMS INTERNATIONAL, INC. ARE URGED TO READ THE PROXY STATEMENT AND OTHER DOCUMENTS THAT HAVE BEEN (OR MAY BE) FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY BECAUSE THEY CONTAIN IMPORTANT INFORMATION. The definitive proxy statement has been mailed to stockholders of CSG Systems International, Inc. Investors and security holders may obtain free copies of these documents and other documents filed with the SEC by CSG Systems International, Inc. through the website maintained by the SEC at http://www.sec.gov. Copies of the documents filed with the SEC by CSG Systems International, Inc. will be available free of charge on CSG Systems International, Inc.'s internet website at https://ir.csgi.com/investor-home/default.aspx or upon written request to: CSG Systems International, Inc., Investor Relations, 169 Inverness Dr W, Suite 300, Englewood, CO 80112 or by email to [email protected].

Participants in Solicitation

CSG Systems International, Inc., its directors and certain of its executive officers and employees may be deemed to be participants in the solicitation of proxies in connection with the proposed transaction. Information about the directors and executive officers of CSG Systems International, Inc. is set forth in the proxy statement filed with the SEC on December 16, 2025 and its proxy statement for its 2025 annual meeting of stockholders, which was filed with the SEC on April 1, 2025.

Additional information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, is contained in the proxy statement relating to the proposed transaction and other relevant materials filed with the SEC. These documents can be obtained free of charge from the sources indicated above.

CSG Systems International, Inc.

Investor Relations

169 Inverness Dr W, Suite 300, Englewood, CO 80112

[email protected]

https://ir.csgi.com/investor-home/default.aspx

This email is being sent to employees of CSG.

FORWARD-LOOKING STATEMENTS

This Form 8-K contains "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. Forward-looking statements include, but are not limited to, statements concerning the Company's expectations, plans, intentions, strategies or prospects with respect to the proposed Merger. These statements are often identified by the use of words such as "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "plan," "hope," "hopeful," "likely," "may," "optimistic," "possible," "potential," "preliminary," "project," "should," "will," "would" or the negative or plural of these words or similar expressions or variations. Forward-looking statements are made based upon management's current expectations and beliefs and are not guarantees of future performance. Such forward-looking statements are subject to a number of risks, uncertainties, assumptions and other factors that could cause actual results and the timing of certain events to differ materially from future results expressed or implied by the forward-looking statements. These factors include, among others: (i) the ability of the parties to complete the proposed transaction on the anticipated terms and timing, or at all, (ii) the satisfaction or waiver of other conditions to the completion of the proposed transaction, including obtaining required shareholder and regulatory approvals; (iii) the risk that the Company's stock price may fluctuate during the pendency of the proposed transaction and may decline if the proposed transaction is not completed; (iv) potential litigation relating to the proposed transaction that could be instituted against the Company or its directors, managers or officers, including the delay, expense or other effects of any outcomes related thereto; (v) the risk that disruptions from the proposed transaction will harm the Company's business, including current plans and operations, including during the pendency of the proposed transaction; (vi) the ability of the Company to retain, motivate, and hire key personnel; (vii) the diversion of management's time and attention from ordinary course business operations to completion of the proposed transaction and integration matters; (viii) potential adverse reactions or changes to business relationships resulting from the announcement, pendency or completion of the proposed transaction; (ix) legislative, regulatory and economic developments; (x) potential business uncertainty, including changes to existing business relationships, during the pendency of the proposed transaction that could affect the Company's financial performance; (xi) certain restrictions during the pendency of the proposed transaction that may impact the Company's ability to pursue certain business opportunities or strategic transactions; (xii) unpredictability and severity of catastrophic events, including but not limited to acts of terrorism, outbreaks of war or hostilities or global pandemics, as well as management's response to any of the aforementioned factors; (xiii) the possibility that the proposed transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events; (xiv) unexpected costs, liabilities or delays associated with the transaction; (xv) the response of competitors to the transaction; (xvi) the occurrence of any event, change or other circumstance that could give rise to the termination of the proposed transaction, including in circumstances requiring the Company to pay a termination fee; (xvii) the ability to realize the anticipated benefits of the Merger, including the expected synergies and cost saving; (xviii) the possibility that competing or superior acquisition proposals for the Company will be made; and (xix) other risks set forth under the heading "Risk Factors," of the Company's Annual Report on Form 10-K for the year ended December 31, 2024 and in the Company's subsequent filings with the Securities and Exchange Commission ("SEC"). You should not rely upon forward-looking statements as predictions of future events. Actual results and outcomes could differ materially from the results described in or implied by such forward looking statements. Forward-looking statements speak only as of the date hereof, and, except as required by law, the Company undertakes no obligation to update or revise these forward-looking statements.

ADDITIONAL INFORMATION AND WHERE TO FIND IT

This communication does not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities or a solicitation of any vote or approval. This communication relates to a proposed acquisition of the Company by Parent. In connection with this proposed acquisition, the Company plans to file one or more proxy statements or other documents with the SEC. This communication is not a substitute for any proxy statement or other document that the Company may file with the SEC in connection with the proposed transaction.

INVESTORS AND SECURITY HOLDERS OF THE COMPANY ARE URGED TO READ THE PROXY STATEMENT AND OTHER DOCUMENTS THAT MAY BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION. The definitive proxy statement has been mailed to stockholders of CSG Systems International, Inc. Investors and security holders may obtain free copies of these documents and other documents filed with the SEC by CSG Systems International, Inc. through the website maintained by the SEC at http://www.sec.gov. Copies of the documents filed with the SEC by the Company will be available free of charge on the Company's internet website at https://ir.csgi.com/investor-home/default.aspx or upon written request to: CSG Systems International, Inc., Investor Relations, 169 Inverness Dr W, Suite 300, Englewood, CO 80112, or by email at [email protected].

PARTICIPANTS IN SOLICITATION

CSG Systems International, Inc., its directors and certain of its executive officers and employees may be deemed to be participants in the solicitation of proxies in connection with the proposed transaction. Information about the directors and executive officers of CSG Systems International, Inc. is set forth in the proxy statement filed with the SEC on December 16, 2025 and its proxy statement for its 2025 annual meeting of stockholders, which was filed with the SEC on April 1, 2025.

Additional information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, is contained in the proxy statement relating to the proposed transaction and other relevant materials filed with the SEC. These documents can be obtained free of charge from the sources indicated above.