SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                                (AMENDMENT NO. )*

                            MGC COMMUNICATIONS, INC.
- --------------------------------------------------------------------------------
                                (Name of Issuer)

                                  COMMON STOCK
- --------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    55276330
- --------------------------------------------------------------------------------
                                 (CUSIP Number)

Check the following box if a fee is being paid with this |_|  statement.  (A fee
is not required only if the filing person:  (1) has a previous statement on file
reporting  beneficial  ownership  of more  than  five  percent  of the  class of
securities  described  in Item 1;  and (2) has  filed  no  amendment  subsequent
thereto reporting  beneficial  ownership of five percent or less of such class.)
(See Rule 13d-7.)

*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 the
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).

                        (Continued on following page(s))

                                Page 1 of 4 Pages

SEC 1745 (10-85)





CUSIP NO. 55276330                     13G             PAGE 2 OF 4 PAGES

- --------------------------------------------------------------------------------
1    NAME OF REPORTING PERSON
     S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

     Massachusetts Financial Services Company ("MFS")
     I.R.S. Identification No.:  04-2747644
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

     (a)   /   /           (b)     /   /
- --------------------------------------------------------------------------------
3    SEC USE ONLY
- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
- --------------------------------------------------------------------------------
        NUMBER OF        5    SOLE VOTING POWER

           SHARES             3,441,186 shares of common stock**

     BENEFICIALLY
- --------------------------------------------------------------------------------

         OWNED BY        6    SHARED VOTING POWER

             EACH
- --------------------------------------------------------------------------------

        REPORTING        7    SOLE DISPOSITIVE POWER

           PERSON             3,633,046 shares of common stock**

             WITH
- --------------------------------------------------------------------------------
8    SHARED DISPOSITIVE POWER

- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     3,633,046 shares of common stock** of which shares are also beneficially
     owned by certain other non-reporting entities as well as MFS.

- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

     10.1% (as calculated pursuant to Rule 13d-3(d)(1)(i))
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*
     IA
- --------------------------------------------------------------------------------
**These 3,441,186 shares of common stock include 250,909 shares which may be
  acquired through the conversion of convertible bonds.

                      *SEE INSTRUCTION BEFORE FILLING OUT!





SCHEDULE 13G                                           PAGE 3 OF 4 PAGES

ITEM 1:   (a)   NAME OF ISSUER:

                MGC Communications, Inc.

          (b)   ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES:

                175 Sully's Trail, Suite 300
                Pittsford, NY  14534

ITEM 2:   (a)   NAME OF PERSON FILING:

                Massachusetts Financial Services Company ("MFS")

          (b)   ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE:

                500 Boylston Street
                Boston, MA  02116

          (c)   CITIZENSHIP:

                See Item 4 on page 2

          (d)   TITLE OF CLASS OF SECURITIES:

                Common Stock

          (e)   CUSIP NUMBER:

                55276330

ITEM 3:         See Item 12 on page 2

ITEM 4:   (a)   AMOUNT BENEFICIALLY OWNED:

                See Item 9 on page 2

          (b)   PERCENT OF CLASS:

                See Item 11 on page 2

          (c)   NUMBER OF SHARES AS TO WHICH SUCH PERSON HAS VOTING AND
                DISPOSITIVE POWERS:

                See Items 5 and 7 on page 2





SCHEDULE 13G                                           PAGE 4 OF 4 PAGES

ITEM 5:         OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS:

                Inapplicable

ITEM 6:         OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER
                PERSON:

                Inapplicable

ITEM 7:         IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH
                ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING
                COMPANY:

                Inapplicable

ITEM 8:         IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP:

                Inapplicable

ITEM 9:         NOTICE OF DISSOLUTION OF GROUP:

                Inapplicable

ITEM 10:        CERTIFICATION:

                By signing  below I certify that to the best of my knowledge and
belief, the securities referred to above were acquired in the ordinary course of
business  and were not acquired for the purpose of and do not have the effect of
changing or  influencing  the control of the issuer of such  securities and were
not acquired in connection  with or as a participant in any  transaction  having
such purposes or effect.

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

Date:  August 18, 2000

Massachusetts Financial Services Company



By:  STEPHEN E. CAVAN
     Stephen E. Cavan
     Senior Vice President,
     Secretary and general counsel