<PAGE>

                                                                    Exhibit 4.31

                                                                  CONFORMED COPY

                              SECOND AMENDMENT TO
                              -------------------
                          WAIVER TO CREDIT AGREEMENT
                          --------------------------

          This SECOND AMENDMENT TO WAIVER TO CREDIT AGREEMENT is dated as of
March 30, 2001 (the "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, 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, the Lenders and the Agent are parties to that
certain Waiver to Credit Agreement dated as of March 30, 2001, as amended by
that certain Amendment to Waiver to Credit Agreement dated as of March 30, 2001
(as so amended, the "Waiver") pursuant to which the Lenders and the Agent waived
                     ------
Borrowers' compliance with certain of the provisions of the Agreement; and

          WHEREAS, the Borrowers have requested the Agent and the Lenders to
supplement the Waiver in certain respects to waive compliance with certain
related 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 Amendment are used as defined in the Agreement.

          Section 2.  Amendments to Waiver.
                      --------------------

          2.1     Section 2.1 of the Waiver is hereby amended in its entirety to
read as follows:

                  2.1    On the condition that the Borrowers shall deliver such
          audited
<PAGE>

          financial statements to the Agent and each of the Lenders on or prior
          to June 30, 2001, the Lenders hereby waive the provisions of Sections
          5.1(a) and 5.1(c) 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, all as audited for the Borrowers and their
          Subsidiaries by their current independent auditor, and the failure of
          the Borrowers to deliver the financial certifications required to
          accompany such financial statements in accordance with Section 5.1(c).
          The Borrowers' failure to deliver such audited financial statements to
          the Agent and each of the Lenders, together with the opinion of such
          accountants, Financial Officer certifications and other certificates
          as required pursuant to Sections 5.1(a) and 5.1(c), on or prior to
          June 30, 2001 shall constitute a default in Borrowers' performance of
          Sections 5.1(a) and 5.1(c). The foregoing waiver is effective only in
          this specific instance, and the Borrowers hereby acknowledge their
          obligations under Sections 5.1(a) and 5.1(c) of the Agreement and
          acknowledge that the foregoing waiver shall not in any way waive
          compliance with the provisions of Sections 5.1(a) and 5.1(c) of the
          Agreement for fiscal year 2001 or thereafter.

          2.2  Section 2.2 of the Waiver is hereby amended in its entirety to
read as follows:

               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 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.  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 year ended December

                                       2
<PAGE>

          31, 2000 pursuant to Section 5.1(a) of the Agreement and 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.

          2.3  Section 2.3 of the Waiver is hereby amended in its entirety to
read as follows:

               2.3  To the extent, but solely to the extent, that Sections 6.3,
          6.4, 6.9 or 6.11 otherwise preclude the Borrowers or their
          Subsidiaries from entering into such transaction, the Lenders hereby
          waive the provisions of Sections 6.9 or 6.11 of the Agreement solely
          to the extent necessary to permit ICG Holdings, Inc. to execute,
          deliver and perform an agreement providing for: (a) the application of
          a $10,000,000 security deposit made by ICG Holdings, Inc. under that
          certain Commercial Lease dated as of January 15, 1998 (the "TriNet
                                                                      ------
          Lease") with TriNet Essential Facilities X, Inc. to cure various
          -----
          defaults under such lease by ICG Holdings, Inc.; (b) a release of ICG
          Holdings, Inc. from any obligation to pay for the garage construction
          described therein, which garage is located at 161 Inverness Drive
          West, Englewood, Colorado; (c) completion of the garage construction
          described therein; and (d) extension of the lease term to twenty five
          (25) years.  Extension of the term of the TriNet Lease to twenty five
          (25) years shall cause the TriNet Lease to constitute a Capitalized
          Lease under the Agreement and, accordingly, ICG Holdings, Inc.'s
          obligations under the TriNet Lease shall constitute Indebtedness which
          is not otherwise permitted under Section 6.3 of the Agreement.
          Lenders acknowledge that certain of the monies constituting the
          security deposit under the TriNet Lease shall be used to satisfy
          obligations secured by mechanics liens which encumber the referenced
          garage, but the foregoing waiver shall not otherwise permit ICG
          Holdings, Inc. or any other Borrower to make any payments in respect
          of such mechanics liens.  Application of such security deposit as
          described above shall not constitute a Capital Expenditure by ICG
          Holdings, Inc. for the purposes of Section 6.4 of the Agreement.

          The Lenders have agreed to the foregoing waiver in part in reliance
          upon a representation by the Borrowers that the guaranteed maximum
          price to complete construction of the referenced garage is
          approximately $7,600,000, which cost includes satisfaction of all
          obligations currently secured by mechanics liens which encumber such
          property.  Borrowers hereby acknowledge and agree that it shall
          constitute an Event of Default under the Agreement in the event that
          ICG Holdings, Inc. or any other Borrower or any of their respective
          Subsidiaries are obligated to pay $500,000 or more (in the aggreate)
          in construction costs in respect of the referenced garage other than
          through the application of the referenced $10,000,000 security
          deposit.

                                       3
<PAGE>

          The foregoing waiver is effective only in this specific instance, and
          the Borrowers hereby acknowledge their obligations under Sections 6.3,
          6.4, 6.9 and 6.11 of the Agreement, and the Borrowers hereby
          acknowledge that the foregoing waiver shall not in any way waive
          compliance with any other provisions of the Agreement.

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

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

          Section 4.  Full Force and Effect.  Except as specifically amended
                      ---------------------
hereby, all of the terms and conditions of the Waiver and the Agreement shall
remain in full force and effect, and the same are hereby ratified and confirmed.
No reference to this Amendment need be made in any instrument or document at any
time referring to the Waiver, a reference to the Waiver in any of such to be
deemed to be a reference to the Waiver as amended hereby.

          Section 5.  Counterparts.  This 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 6.  Headings.  The various headings of this Amendment are
                      --------
inserted for convenience only and shall not affect the meaning or interpretation
of this Amendment or any provisions hereof.

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


<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this 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:  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

                                       5
<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

                                       6
<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

                                       7
<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

                                       8
<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

                                       9
<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

                                       10