Document:

<PAGE>

                                                                    Exhibit 4.28

                                                                  CONFORMED COPY
                              FIRST AMENDMENT TO
                              ------------------
                               CREDIT AGREEMENT
                               ----------------

           This FIRST AMENDMENT TO CREDIT AGREEMENT dated as of January 31, 2001
(the "First Amendment"), is entered into by and among ICG COMMUNICATIONS, INC.,
      ---------------
a Delaware corporation, and each of its direct and indirect subsidiaries party
to the Agreement (as defined below) (each, individually, a "Borrower" and
                                                            --------
collectively, the "Borrowers"), THE CHASE MANHATTAN BANK, a New York banking
                   ---------
corporation, and each of the other commercial banks, finance companies,
insurance companies or other financial institutions or funds from time to time
party to the Agreement (as defined below) (the "Lenders"), and THE CHASE
                                                -------
MANHATTAN BANK, as agent (the "Agent").
                               -----

                                  WITNESSETH:

           WHEREAS, the Borrowers, the Lenders and the Agent are parties to that
certain Revolving Credit Agreement dated as of December 4, 2000 (the
"Agreement"), pursuant to which the Lenders have made available to the Borrowers
 ---------
a revolving credit and letter of credit facility in an aggregate principal
amount not to exceed $350,000,000 and initially not to be less than
$200,000,000; and

           WHEREAS, the Borrowers have requested that the Lenders make certain
modifications to the Agreement; and

           WHEREAS, the Borrowers and the Lenders desire to amend and supplement
the Agreement to reflect the modifications requested by the Borrowers;

           NOW, THEREFORE, in consideration of the premises and the mutual
agreements herein set forth and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

           Section 1. Definitions. Capitalized terms used and not otherwise
                      -----------
defined in this First Amendment are used as defined in the Agreement.

           Section 2. Amendments to Agreement. Subject to the conditions set
                      -----------------------
forth in Section 3 hereof, the Agreement is hereby amended as follows:
         ---------

           2.1 Section 7.1(m) of the Agreement is hereby amended by modifying
clause "(iii)" to read as follows: "mechanics liens and certain other
pre-petition claims against the Borrowers in a total amount not in excess of
$17,000,000 (excluding refunds or credits to customers issued in the ordinary
course of business)".

           Section 3. Effectiveness. The effectiveness of this First Amendment
                      -------------
is subject to the satisfaction and occurrence of the following conditions
precedent:
<PAGE>

           3.1 The Agent shall have received executed counterparts of this First
      Amendment which, when taken together, bear the signatures of the Borrowers
      and the Required Lenders.

           Section 4. Representations and Warranties. Each Borrower represents
                      ------------------------------
and warrants to the Lenders that:

           4.1 The representations and warranties of the Borrowers contained in
      Section 3 of the Agreement are correct in all material respects on and as
      of the date hereof as if such representations and warranties had been made
      on and as of the date hereof (except to the extent that any such
      representations and warranties specifically relate to an earlier date);
      and

           4.2 After giving effect to the amendments contained herein, (i) each
      Borrower is in compliance with all the terms and provisions set forth in
      the Agreement, and (ii) no Event of Default has occurred and is continuing
      (other than as specifically waived herein) or would result from the
      execution, delivery and performance of this First Amendment.

           Section 5. Full Force and Effect. Except as specifically amended
                      ---------------------
hereby, all of the terms and conditions of the Agreement shall remain in full
force and effect, and the same are hereby ratified and confirmed. No reference
to this First Amendment need be made in any instrument or document at any time
referring to the Agreement, a reference to the Agreement in any of such to be
deemed to be reference to the Agreement as amended hereby.

           Section 6. Counterparts. This First Amendment may be executed in any
                      ------------
number of counterparts, each of which shall constitute an original, but all of
which taken together shall constitute one and the same agreement.

           Section 7. Headings. The various headings of this First Amendment are
                      --------
inserted for convenience only and shall not affect the meaning or interpretation
of this First Amendment or any provisions hereof.

            [The remainder of this page is intentionally left blank.]

                                       2
<PAGE>

           IN WITNESS WHEREOF, the parties hereto have caused this First
Amendment to be duly executed as of the day and the year first written.

                             BORROWERS:

                             ICG COMMUNICATIONS, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             ICG TEVIS, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             ICG FUNDING, LLC

                             By:     ICG Communications, Inc.,
                                     its Managing Member

                                     By: /s/ Bernard L. Zuroff
                                         -------------------------------
                                     Name:   Bernard L. Zuroff
                                     Title:  Vice President

                             ICG SERVICES, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                             ICG MOUNTAIN VIEW, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                                       3
<PAGE>

                             ICG NETAHEAD, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                             ICG EQUIPMENT, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                             ICG CANADIAN ACQUISITION, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                             ICG HOLDINGS (CANADA) CO.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                             ICG HOLDINGS, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Executive Vice President

                             ICG TELECOM GROUP, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                                       4
<PAGE>

                             NIKONET, LLC

                             By:   ICG Telecom Group, Inc.,
                                   its Managing Member

                                   By: /s/ Bernard L. Zuroff
                                       -------------------------------
                                   Name:   Bernard L. Zuroff
                                   Title:  Vice President

                             ICG OHIO LINX, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             ICG ENHANCED SERVICES, INC.

                             By: /s/ Bernard L. Zuroff
                                 --------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             COMMUNICATIONS BUYING GROUP, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             ICG TELECOM GROUP OF VIRGINIA, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                                       5
<PAGE>

                             ICG DATACHOICE NETWORK SERVICES, L.L.C.

                             By:   ICG Telecom Group, Inc.,
                                   its Managing Member

                                   By: /s/ Bernard L. Zuroff
                                       -------------------------------
                                   Name:   Bernard L. Zuroff
                                   Title:  Vice President

                             PTI HARBOR BAY, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             BAY AREA TELEPORT, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             ICG ACCESS SERVICES - SOUTHEAST, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                             TRANS AMERICAN CABLE, INC.

                             By: /s/ Bernard L. Zuroff
                                 -------------------------------
                             Name:   Bernard L. Zuroff
                             Title:  Vice President

                                       6
<PAGE>

                             ICG TELECOM OF SAN DIEGO, L.P.

                             By:      ICG Telecom Group, Inc.,
                                      its General Partner

                                      By: /s/ Bernard L. Zuroff
                                          -------------------------------
                                      Name:   Bernard L. Zuroff
                                      Title:  Vice President

                             WESTERN PLAINS FINANCE, L.L.C.

                             By:      ICG Telecom Group, Inc.,
                                      its Managing Member

                                      By: /s/ Bernard L. Zuroff
                                          -------------------------------
                                      Name:   Bernard L. Zuroff
                                      Title:  Vice President

                             ICG CHOICECOM MANAGEMENT, LLC

                             By:      ICG Telecom Group, Inc.,
                                      its Managing Member

                                      By: /s/ Bernard L. Zuroff
                                          -------------------------------
                                      Name:   Bernard L. Zuroff
                                      Title:  Vice President

                             ICG CHOICECOM, L.P.

                             By:      ICG ChoiceCom Management, LLC
                                      its General Partner

                                      By:      ICG Telecom Group, Inc.,
                                               its Managing Member

                                               By: /s/ Bernard L. Zuroff
                                                   --------------------------
                                               Name:   Bernard L. Zuroff
                                               Title:  Vice President

                                       7
<PAGE>

                            DOWNNORTH, INC.

                            By: /s/ Bernard L. Zuroff
                                ---------------------------
                            Name:   Bernard L. Zuroff
                            Title:  Vice President

                            THE CHASE MANHATTAN BANK,
                            Individually and as Agent

                            By: /s/ Norma C. Corio
                               ----------------------------
                            Name:   Norma C. Corio
                            Title:  Managing Director

                                       8<PAGE>

                                                                    Exhibit 4.29

                                                                  CONFORMED COPY
                                                                  --------------

                           WAIVER TO CREDIT AGREEMENT
                           --------------------------

           This WAIVER TO CREDIT AGREEMENT dated as of March 30, 2001 (the
"Waiver"), is entered into by and among ICG COMMUNICATIONS, INC., a Delaware
 ------
corporation, and each of its direct and indirect subsidiaries party to the
Agreement (as defined below) (each, individually, a "Borrower" and collectively,
                                                     --------
the "Borrowers"), THE CHASE MANHATTAN BANK, a New York banking corporation, and
     ---------
each of the other commercial banks, finance companies, insurance companies or
other financial institutions or funds from time to time party to the Agreement
(as defined below) (the "Lenders"), and THE CHASE MANHATTAN BANK, as agent (the
                         -------
"Agent").
 -----

                                   WITNESSETH:

           WHEREAS, the Borrowers, the Lenders and the Agent are parties to that
certain Revolving Credit Agreement dated as of December 4, 2000, as amended by
that certain First Amendment to Revolving Credit Agreement dated as of January
31, 2001 (as so amended, the "Agreement"), pursuant to which the Lenders have
                              ---------
made available to the Borrowers a revolving credit and letter of credit facility
in an aggregate principal amount not to exceed $350,000,000 and initially not to
be less than $200,000,000; and

           WHEREAS, the Borrowers have requested the Agent and the Lenders to
waive compliance with certain of the provisions of the Agreement; and

           WHEREAS, the Borrowers and the Lenders desire to waive compliance
with certain of the provisions of the Agreement; and

           NOW, THEREFORE, in consideration of the premises and the mutual
agreements herein set forth and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

           Section 1. Definitions. Capitalized terms used and not otherwise
                      -----------
defined in this Waiver are used as defined in the Agreement.

           Section 2. Waivers Under the Agreement.
                      ---------------------------

           2.1 On the condition that the Borrowers shall deliver such financial
statements to the Agent and each of the Lenders on or prior to April 13, 2001,
the Lenders hereby waive the provisions of Section 5.1(a) of the Agreement
solely to the extent necessary to waive the failure of the Borrowers to deliver
to the Agent and each of the Lenders within ninety (90) days after the end of
fiscal year 2000 the Borrowers' consolidated and consolidating balance sheets
and related statements of income, stockholders' equity and cash flows for fiscal
year 2000. The Borrowers' failure to deliver such financial statements to the
Agent and each of the Lenders on or prior to

                                       1
<PAGE>

April 13, 2001 shall constitute a default in Borrowers' performance of Section
5.1(a). The foregoing waiver is effective only in this specific instance, and
the Borrowers hereby acknowledge their obligations under Section 5.1(a) of the
Agreement and acknowledge that the foregoing waiver shall not in any way waive
compliance with the provisions of Section 5.1(a) of the Agreement for fiscal
year 2001 or thereafter.

           2.2 The Lenders hereby waive the provisions of Sections 5.1(a),
5.1(b) and 5.6(a) of the Agreement solely to the extent necessary to waive: (a)
the failure by the Borrowers and their Subsidiaries to maintain or cause to be
maintained true and complete books and records in accordance with GAAP of the
financial operations of the Borrowers and their Subsidiaries at all times prior
to June 30, 2001; and (b) any default or Event of Default resulting from
delivery by the Borrowers' current independent auditor of an opinion in respect
of the Borrowers' and their Subsidiaries' financial statements for the fiscal
year ended December 31, 2000 which is qualified or adverse as a result of such
failure. The foregoing waiver relates solely to the failure by the Borrowers and
their Subsidiaries to comply with the provisions of Financial Accounting
Standards Board Statement No. 121, "Accounting for Impairment of Long-Lived
Assets and for Long-Lived Assets To Be Disposed Of " ("FAS 121") as described in
                                                       -------
the draft auditor's opinion previously delivered to the Agent, and shall not
relate to any other non-compliance of such financial statements with the
provisions of GAAP. The foregoing waiver is effective only in the specific
instances referenced herein and the Borrowers hereby acknowledge their
obligations under Sections 5.1(a), 5.1(b) and 5.6 and acknowledge that the
foregoing waiver shall not in any way waive compliance with the provisions of
such Sections for the purposes of delivery of financial statements prepared in
accordance with GAAP for any and all accounting periods ending on or after June
30, 2001. The Borrowers hereby further acknowledge that the foregoing waiver of
Borrowers' obligations under Section 5.6 of the Agreement relates solely to
non-compliance with the provisions of FAS 121 and shall not in any way waive
Borrowers' compliance with Section 5.6 at all times from and after June 30,
2001. Accordingly, the Borrowers hereby covenant and agree that the financial
statements to be delivered by the Borrowers for the fiscal quarter ending June
30, 2001 pursuant to Section 5.1(b) of the Agreement, and all other financial
statements thereafter delivered by the Borrowers pursuant to Sections 5.1(a) and
5.1(b) of the Agreement, shall be prepared in accordance with GAAP, including,
without limitation, FAS 121, subject to normal year-end audit adjustments.

           Section 3. Effectiveness. The effectiveness of this Waiver is subject
                      -------------
to the satisfaction and occurrence of the following conditions precedent:

           3.1 The Agent shall have received executed counterparts of this
      Waiver which, when taken together, bear the signatures of the Borrowers
      and the Lenders.

           Section 4. Representations and Warranties. Each Borrower represents
                      ------------------------------
and warrants to the Lenders that:

           4.1 The representations and warranties of the Borrowers contained in
      Section 3 of the Agreement are true and correct in all material respects
      on and as of the date hereof as if such representations and warranties had
      been made on and as of the date hereof (except to the extent that any such
      representations and warranties specifically relate to an earlier date

                                       2
<PAGE>

      and except that references to Schedule 3.13 of the Agreement shall mean
                                    -------------
      Schedule 3.13 attached hereto as Exhibit A and except with respect to
      -------------                    ---------
      Section 3.4 to the extent that such compliance with GAAP is specifically
      -----------
      waived herein); and

           4.2 After giving effect to the waivers contained herein, (i) each
      Borrower is in compliance with all the terms and provisions set forth in
      the Agreement, and (ii) no Event of Default has occurred and is continuing
      (other than as specifically waived herein) or would result from the
      execution, delivery and performance of this Waiver.

           Section 5. Full Force and Effect. Except as specifically waived
                      ---------------------
hereby, all of the terms and conditions of the Agreement shall remain in full
force and effect, and the same are hereby ratified and confirmed.

           Section 6. Counterparts. This Waiver may be executed in any number of
                      ------------
counterparts, each of which shall constitute an original, but all of which taken
together shall constitute one and the same agreement.

           Section 7. Headings. The various headings of this Waiver are inserted
                      --------
for convenience only and shall not affect the meaning or interpretation of this
Waiver or any provisions hereof.

            [The remainder of this page is intentionally left blank.]

                                       3
<PAGE>

           IN WITNESS WHEREOF, the parties hereto have caused this Waiver to be
duly executed as of the day and the year first written.

                             BORROWERS:

                             ICG COMMUNICATIONS, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG TEVIS, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             ICG FUNDING, LLC

                             By:    ICG Communications, Inc.,
                                    its Managing Member

                                    By:  /s/ Bernard L. Zuroff
                                         --------------------------------
                                    Name:   Bernard L. Zuroff
                                    Title:  Executive Vice President

                             ICG SERVICES, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG MOUNTAIN VIEW, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                                       4
<PAGE>

                             ICG NETAHEAD, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG EQUIPMENT, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG CANADIAN ACQUISITION, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG HOLDINGS (CANADA) CO.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG HOLDINGS, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Executive Vice President

                             ICG TELECOM GROUP, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                                       5
<PAGE>

                             NIKONET, LLC

                             By:    ICG Telecom Group, Inc.,
                                    its Managing Member

                                    By:      /s/ Bernard L. Zuroff
                                             ---------------------------------
                                    Name:    Bernard L. Zuroff
                                    Title:   Vice President

                             ICG OHIO LINX, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             ICG ENHANCED SERVICES, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             COMMUNICATIONS BUYING GROUP, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             ICG TELECOM GROUP OF VIRGINIA, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                                       6
<PAGE>

                             ICG DATACHOICE NETWORK SERVICES, L.L.C.

                             By:    ICG Telecom Group, Inc.,
                                    its Managing Member

                                    By:      /s/ Bernard L. Zuroff
                                             -------------------------------
                                    Name:    Bernard L. Zuroff
                                    Title:   Vice President

                             PTI HARBOR BAY, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             BAY AREA TELEPORT, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             ICG ACCESS SERVICES - SOUTHEAST, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             TRANS AMERICAN CABLE, INC.

                             By:    /s/ Bernard L. Zuroff
                                    ---------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                                       7
<PAGE>

                             ICG TELECOM OF SAN DIEGO, L.P.

                             By:    ICG Telecom Group, Inc.,
                                    its General Partner

                                    By:    /s/ Bernard L. Zuroff
                                           -------------------------------
                                    Name:  Bernard L. Zuroff
                                    Title: Vice President

                             WESTERN PLAINS FINANCE, L.L.C.

                             By:    ICG Telecom Group, Inc.,
                                    its Managing Member

                                    By:    /s/ Bernard L. Zuroff
                                           -------------------------------
                                    Name:  Bernard L. Zuroff
                                    Title: Vice President

                             ICG CHOICECOM MANAGEMENT, LLC

                             By:    ICG Telecom Group, Inc.,
                                    its Managing Member

                                    By:    /s/ Bernard L. Zuroff
                                           ----------------------------
                                           Name:  Bernard L. Zuroff
                                           Title: Vice President

                             ICG CHOICECOM, L.P.

                             By:    ICG ChoiceCom Management, LLC
                                    its General Partner

                                    By:    ICG Telecom Group, Inc.,
                                           its Managing Member

                                           By:/s/ Bernard L. Zuroff
                                              ---------------------
                                              Name:   Bernard L. Zuroff
                                              Title:  Vice President

                                       8
<PAGE>

                             DOWNNORTH, INC.

                             By:    /s/ Bernard L. Zuroff
                                    -------------------------------------
                             Name:  Bernard L. Zuroff
                             Title: Vice President

                             THE CHASE MANHATTAN BANK,
                             Individually and as Agent

                             By:    /s/ Norma C. Corio
                                    ------------------------------------
                             Name:  Norma C. Corio
                             Title: Managing Director

                                       9
<PAGE>

                                    EXHIBIT A
                                    ---------

                                  Schedule 3.13
                                  -------------

                                       10

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00027-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00027-of-00352.parquet"}]]