UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 20)

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report this acquisition that is the subject of this Schedule 13D, and is filing this Schedule because of Rule 13d-1(e), Rule 13d-1(f) or Rule 13d-1(g), check the following box:  ¨

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act.

SCHEDULE 13D/A20

This constitutes Amendment No. 20 (the “Amendment No. 20”) to the Statement on Schedule 13D, filed on behalf of Karen Singer (“Ms. Singer”), dated February 28, 2008 (the “Statement”), relating to the common stock (the “Common Stock”) of Evolving Systems, Inc., a Delaware corporation (the “Issuer” or “Company”). Unless specifically amended or modified hereby, the disclosure set forth in the Statement shall remain unchanged.

Item 4. Purpose of the Transaction.

Item 4 of the Statement is hereby amended and restated in its entirety as follows:

As previously disclosed, on November 26, 2010, Ms. Singer entered into a Confidentiality Agreement, in the form previously filed as Exhibit 99.1 to Schedule 13D (the “Previous Confidentiality Agreement”), between the Issuer and Ms. Singer. The Previous Confidentiality Agreement provided that, subject to certain exceptions set forth therein, the Trust would keep confidential certain information received by the Trust from the Issuer. As disclosed previously, Ms. Singer entered into the Previous Confidentiality Agreement in connection with the Trust’s ongoing discussions with the Company regarding governance and enhancing shareholder value. The term of the Previous Confidentiality Agreement was extended several times and, effective April 22, 2011, the Previous Confidentiality Agreement was amended to extend further the period during which it remained effective so that, as so amended, the Previous Confidentiality Agreement remained in effect until June 30, 2011. Effective July 15, 2011, the Previous Confidentiality Agreement was reinstated and, as so reinstated, the Previous Confidentiality Agreement was further amended to extend the period during which it remained effective until August 15, 2011. Effective June 8, 2012, Ms. Singer and the Company entered into a Confidentiality Agreement (the “June 2012 Confidentiality Agreement”) in connection with further discussions between the Trust and the Company regarding enhancing shareholder value. The June 2012 Confidentiality Agreement remains in effect until September 30, 2012 and otherwise contains substantially the same terms and conditions as were contained in the Previous Confidentiality Agreement.

Except as described above in this Item 4 and herein, Ms. Singer does not currently have any specific plans or proposals that relate to or would result in any of the actions or events specified in clauses (a) through (j) of Item 4 of Schedule 13D. Ms. Singer reserves the right to change plans and take any and all actions that Ms. Singer may deem appropriate to maximize the value of her investments, including, among other things, purchasing or otherwise acquiring additional securities of the Issuer, selling or otherwise disposing of any securities of the Issuer beneficially owned by her, in each case in the open market or in privately negotiated transactions, or formulating other plans or proposals regarding the Issuer or its securities to the extent deemed advisable by Ms. Singer in light of her general investment policies, market conditions, subsequent developments affecting the Issuer and the general business and future prospects of the Issuer. Ms. Singer may take any other action with respect to the Issuer or any of the Issuer’s debt or equity securities in any manner permitted by applicable law.

Item 4 of this Schedule 13D/A is incorporated herein by reference.

SIGNATURES

After reasonable inquiry and to the best of the undersigned’s knowledge and belief, the undersigned hereby certifies that the information set forth in this statement is true, complete and correct.

Dated: June 12, 2012

4

Exhibit 99.1

CONFIDENTIALITY AGREEMENT

This Confidentiality Agreement (this “Agreement”) is entered into as of the 8th day of June, 2012, by and between Evolving Systems, Inc. (“Evolving Systems”) and Karen Singer, as Trustee of the Singer Children’s Management Trust and Gary Singer (collectively, “Recipient”).

RECITALS

In consideration of the above and the covenants contained in this Agreement, the parties agree as follows:

For purposes of this Agreement, the term “Confidential Information” means any and all oral, written or electronic information which is made available to Recipient by Evolving Systems during the term of this Agreement regardless of the manner in which such information is furnished. The term “Confidential Information” does not include, however, any information which (a) at the time of disclosure by Evolving Systems, or thereafter, is generally available to the public (other than as a result of a disclosure made directly or indirectly by Recipient), (b) was available to the Recipient on a non-confidential basis from a source other than Evolving Systems (provided that such source is not or was not known to be bound by a confidentiality agreement with Evolving Systems), or (c) has been shown by reasonably acceptable evidence to have been independently acquired or developed by the Recipient without violating any of the Recipient’s obligations under Section 2 below.

The Confidential Information will not be disclosed to third parties and will be kept confidential by the Recipient. Notwithstanding the preceding sentence, Recipient may disclose the Confidential Information or portions thereof to those of Recipient’s advisors (“Representatives”) who need to know such information for the purpose of providing advice to Recipient, if Recipient (i) informs such Representative of the confidential nature of the Confidential Information and (ii) secures the agreement of such Representative to the terms and conditions of this agreement.

In the event that Recipient becomes legally compelled to disclose any Confidential Information, Recipient shall provide Evolving Systems with prompt notice before such Confidential Information is disclosed so that Evolving Systems may, at the sole cost and expense of Evolving Systems, seek a protective order or other appropriate remedy or waive compliance with the provisions of this Agreement. In the event that such protective order or other remedy is not obtained, Recipient shall furnish only that portion of the Confidential Information which Recipient is advised by counsel that Recipient is legally required to provide and shall exercise, at the sole cost and expense of Evolving Systems, Recipient’s reasonable efforts to assist Evolving Systems in obtaining a protective order or other reliable assurance that confidential treatment will be accorded to the Confidential Information that is required to be disclosed.

At any time upon the request of Evolving Systems, Recipient agrees to return promptly all copies, extracts or other reproductions in whole or in part of the Confidential Information in his possession to Evolving Systems, and Recipient agrees to destroy all copies of any memoranda, notes, analysis, compilations, studies or other documents prepared by Recipient based on, containing or reflecting any Confidential Information, except that one copy of such materials may be retained by Recipient’s counsel for the purpose of documenting the materials Recipient has received. Such destruction shall, if requested, be certified in writing to Evolving Systems.

(a) No provision in this Agreement may be waived or amended except by written consent of Evolving Systems and the Recipient. It is further understood and agreed that no failure or delay by Evolving Systems or Recipient in exercising any right, power or privilege hereunder will operate as a waiver thereof, nor will any single or partial exercise or waiver of a right, power or privilege preclude any other or further exercise thereof.

(b) This Agreement will be effective through September 30, 2012. No such termination shall affect the application of this Agreement to any disclosures made prior to the termination of this Agreement.

To protect the Confidential Information and in order for Evolving Systems to enforce its rights under this Agreement, Evolving Systems shall be entitled to a temporary restraining order, a preliminary injunction, or a permanent injunction by any court of competent jurisdiction to enjoin and restrain the unauthorized disclosure or use of any Confidential Information, or other violation of this Agreement, and these rights shall be cumulative to any other rights Evolving Systems might have.

Recipient understands that during the term of this Agreement they may be exposed to business plans, forecasts and other information that may constitute “material, non-public information” of Evolving Systems. In addition to the restrictions provided for in this Agreement, use or disclosure of such information may give rise to liability under U.S. Federal securities laws. Therefore, but without limiting the provisions of Section 5(b) hereof, Recipient acknowledges that, so long as they are in possession of material non-public information about Evolving Systems, they will comply with applicable federal and state securities laws with respect to purchases and sales of Evolving Systems’ securities.

a. This Agreement constitutes the entire agreement between the parties hereto with respect to the subject matter described in this Agreement. This Agreement may be waived, amended or modified only by an instrument in writing signed by the party against which such waiver, amendment or modification is sought to be enforced.

b. In case any one or more of the provisions contained in this Agreement shall be held to be unenforceable in any respect, such unenforceability shall not affect any other provision of this Agreement.

c. Section headings contained in this Agreement are for reference purposes only and shall not affect the meaning or interpretation of any provision of this Agreement.

d. This Agreement shall be governed by the laws of the State of Delaware.

e. Neither party to this Agreement may transfer or assign its rights under this Agreement without the prior written consent of the other party. The agreement shall continue for the benefit of and shall be binding upon the successors and permitted assigns of each party.

f. PDF or faxed copies of this Agreement, signed by each of the parties, shall be enforceable as originals.

IN WITNESS WHEREOF, the parties have executed this Agreement on the day and year first above written.