SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                -----------------

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                               (Amendment No.) /1/

                             Pac-West Telecomm, Inc.
                                (Name of Issuer)

                    Common Stock, par value $0.001 per share
                         (Title of Class of Securities)

                                   69371Y 10 1
                                 (CUSIP Number)

                                December 31, 2008
             (Date of Event Which Requires Filing of This Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

     [_] Rule 13d-1(b)

     [_] Rule 13d-1(c)

     [X] Rule 13d-1(d)

-----------
     /1/ The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which would
alter disclosures provided in a prior cover page.

     The information required in 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 (however, see
the Notes).



------------------------                                  ----------------------
 CUSIP No.  69371Y 10 1               13G                 Page  2  of  8  Pages
------------------------                                  ----------------------

--------------------------------------------------------------------------------
 1    NAME OF REPORTING PERSON


      William Blair Capital Partners VI, L.P.
--------------------------------------------------------------------------------
 2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions)
                                                                (a) [_]
                                                                (b) [_]
--------------------------------------------------------------------------------
 3    SEC USE ONLY

--------------------------------------------------------------------------------
 4    CITIZENSHIP OR PLACE OF ORGANIZATION

      Delaware
--------------------------------------------------------------------------------
                     5    SOLE VOTING POWER

     NUMBER OF            0

      SHARES       -------------------------------------------------------------
                     6    SHARED VOTING POWER
   BENEFICIALLY
                          0 (See Item 4)
     OWNED BY      -------------------------------------------------------------
       EACH          7    SOLE DISPOSITIVE POWER

    REPORTING             0

      PERSON       -------------------------------------------------------------
                     8    SHARED DISPOSITIVE POWER
       WITH
                          0 (See Item 4)
--------------------------------------------------------------------------------
 9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      0 (See Item 4)
--------------------------------------------------------------------------------
10    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
      (See Instructions)
                                                                    [-]
--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

      0%
--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (See Instructions)

      PN
--------------------------------------------------------------------------------



--------------------------                                ----------------------
 CUSIP No.  69371Y 10 1               13G                 Page  3  of  8  Pages
--------------------------                                ----------------------


--------------------------------------------------------------------------------
 1    NAME OF REPORTING PERSON

      William Blair Capital Partners VI, L.L.C.
--------------------------------------------------------------------------------
 2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions)
                                                                (a) [_]
                                                                (b) [_]
--------------------------------------------------------------------------------
 3    SEC USE ONLY


--------------------------------------------------------------------------------
 4    CITIZENSHIP OR PLACE OF ORGANIZATION

      Delaware
--------------------------------------------------------------------------------
                     5    SOLE VOTING POWER

     NUMBER OF            0

      SHARES       -------------------------------------------------------------
                     6    SHARED VOTING POWER
   BENEFICIALLY
                          0 (See Item 4)
     OWNED BY
                   -------------------------------------------------------------
       EACH          7    SOLE DISPOSITIVE POWER

    REPORTING             0

      PERSON       -------------------------------------------------------------
                     8    SHARED DISPOSITIVE POWER
       WITH
                          0 (See Item 4)
--------------------------------------------------------------------------------
 9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

      0 (See Item 4)
--------------------------------------------------------------------------------
10    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
      (See Instructions)
                                                                    [_]
--------------------------------------------------------------------------------
11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

      0%
--------------------------------------------------------------------------------
12    TYPE OF REPORTING PERSON (See Instructions)

      OO
--------------------------------------------------------------------------------



                                 SCHEDULE 13G

Item 1(a). Name of Issuer:

           Pac-West Telecomm, Inc. (the "Company")

Item 1(b). Address of Issuer's Principal Executive Offices:

           4210 Coronado Avenue
           Stockton, California 95204

Item 2(a). Name of Persons Filing:

          This statement is filed jointly by each of the following Persons
          pursuant to Rule 13d-1(k) promulgated by the Securities and Exchange
          Commission ("SEC") under Section 13 of the Securities Exchange Act of
          1934, as amended (the "Act"): (i) William Blair Capital Partners VI,
          L.P., a Delaware limited partnership (the "Fund"), by virtue of its
          direct beneficial ownership of Common Stock and (ii) William Blair
          Capital Partners VI, L.L.C. ("WBCPCO," together with the Fund, each a
          "Reporting Person" and collectively, "Reporting Persons"), a Delaware
          limited liability company, by virtue of its being the general partner
          of the Fund. By virtue of being members of the Board of Managers of
          WBCPCO (the "Board"), Timothy Burke, John Ettelson, Robert D. Blank,
          David G. Chandler, Edgar D. Jannotta, Arda Minocherhomjee, Timothy M.
          Murray, and Thomas C. Theobald may be deemed to possess indirect
          beneficial ownership of the Common Stock, but such beneficial
          ownership is disclaimed. Only the Board, acting upon the consent of a
          majority of the members of the Board at any meeting of the Board where
          a quorum is present, possesses the right to vote, direct the vote,
          dispose or direct the disposition of the Common Stock. No individual
          has sole power to vote, direct the vote, dispose or direct the
          disposition of the Common Stock. The Reporting Persons have entered
          into an Agreement Related to the Joint Filing of Schedule 13G, dated
          February 20, 2009, a copy of which is filed with this Schedule 13G as
          Exhibit A, pursuant to which the Reporting Persons have agreed to file
          this statement jointly in accordance with the provisions of Rule
          13d-1(k) under the Act. Information with respect to each of the
          Reporting Persons is given solely by such Reporting Person, and no
          Reporting Person assumes responsibility for the accuracy or
          completeness of information provided by another Reporting Person. By
          their signature on this statement, each of the Reporting Persons
          agrees that this statement is filed on behalf of such Reporting
          Person. The Reporting Persons may be deemed to constitute a "group"
          for purposes of Section 13(d)(3) of the Act. The Reporting Persons
          expressly disclaim that they have agreed to act as a group other than
          as described in this statement.

Item 2(b). Address of Principal Business Office or, if none, Residence:

          The address of the principal business office of each of the Reporting
          Persons is 222 West Adams Street, Chicago, Illinois 60606.

Item 2(c). Citizenship:

          The Fund is a Delaware limited partnership and WBCPCO is a Delaware
          limited liability company.

Item 2(d). Title of Class of Securities:

          Common Stock, par value $0.001 per share ("Common Stock").

Item 2(e). CUSIP No.:

          69371Y 10 1

Item 3.   If this statement is filed pursuant to Rules 13d-1(b) or
          13d-2(b) or (c), check whether the person filing is a:

          Not Applicable.

Item 4.   Ownership (as of December 31, 2008):

          As of December 31, 2008, the Fund was the registered owner Of 0 shares
          of Common Stock.

                                  Page 5 of 8



Item 5.  Ownership of Five Percent or Less of a Class:

          As of December 31, 2008, the Fund was the registered owner of 0 shares
          of Common Stock.

Item 6.  Ownership of More Than Five Percent on Behalf of Another
         Person:

          Not Applicable.

Item 7.  Identification and Classification of the Subsidiary Which
         Acquired the Security Being Reported on By the Parent Holding
         Company:

         Not Applicable.

Item 8.  Identification and Classification of Members of the Group:

         Not Applicable.

Item 9.  Notice of Dissolution of a Group:

         Not Applicable.

Item 10. Certification:

         Not Applicable.

                                  Page 6 of 8



                                    SIGNATURE

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

Date: February 20, 2009

                                       William Blair Capital Partners
                                       VI, L.P.

                                       By: William Blair Capital
                                           Partners VI, L.L.C., its
                                           general partner


                                       By: /s/ David G. Chandler
                                           ---------------------------
                                       Its: Managing Director

                                       William Blair Capital Partners
                                       VI, L.L.C.


                                       By: /s/ David G. Chandler
                                           ---------------------------
                                       Its: Managing Director


                                  Page 7 of 8



EXHIBIT A
---------

                    AGREEMENT REGARDING THE JOINT FILING OF
                                 SCHEDULE 13G

                            -----------------------

William Blair Capital Partners VI, L.P. and William Blair Capital Partners VI,
L.L.C. hereby agree that the Statement on Schedule 13G to which this agreement
is attached as an exhibit, as well as all future amendments to such Statement,
shall be filed jointly on behalf of each of them. This agreement is intended to
satisfy the requirements of Rule 13d-1(k)(1)(iii) under the Securities Exchange
Act of 1934, as amended.

Date: February 20, 2009

                                       William Blair Capital Partners
                                       VI, L.P.

                                       By: William Blair Capital
                                           Partners VI, L.L.C., its
                                           general partner


                                       By: /s/ David G. Chandler
                                          ----------------------------

                                       Its: __________________________

                                       William Blair Capital Partners
                                       VI, L.L.C.


                                       By:  /s/ David G. Chandler
                                           ----------------------------

                                       Its: ___________________________

                                  Page 8 of 8