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                                                                  EXECUTION COPY



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                            SHARE EXCHANGE AGREEMENT

                                     BETWEEN

                          QUADRANGLE INVESTMENTS, INC.

                                       AND

                                 ICG TEVIS, INC.



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                                   Dated as of

                                February 28, 2000

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            This SHARE EXCHANGE AGREEMENT is dated as of February 28, 2000 (this
"Agreement"), by and between Quadrangle Investments, Inc. ("Quadrangle"), a
Delaware corporation and a wholly owned subsidiary of Teligent, Inc.
("Teligent"), and ICG Tevis, Inc., a Delaware corporation ("ICG").

            WHEREAS, Quadrangle proposes, subject to the terms and conditions
set forth herein, to sell to ICG 1,000,000 Shares of Class A Common Stock of
Teligent (the "Teligent Stock") in exchange for the ICG Stock referenced below;
and

            WHEREAS, ICG proposes, subject to the terms and conditions set forth
herein, to sell to Quadrangle 2,996,076 shares of its common stock, par value
$0.01 per share of ICG Communications, Inc. (the "ICG Stock"), in exchange for
the Teligent Stock;

            NOW, THEREFORE, the parties hereto, intending to be legally bound,
hereby agree as follows.

                                    ARTICLE I

                                   DEFINITIONS

            As used in this Agreement, the following terms shall have the
following meanings:

            "Applicable Law" means (a) any United States federal, state, local
or foreign law, statute, rule, regulation, order, writ, injunction, judgment,
decree or permit of any Governmental Authority and (b) with respect to any
party, any rule or listing requirement of any applicable national stock exchange
or listing requirement of any national stock exchange or Commission recognized
trading market on which securities issued by such party are listed or quoted.

            "Business Day" means any day other than a Saturday, a Sunday or a
day when banks in The City of New York are authorized by Applicable Law to be
closed.

            "Capital Stock" means with respect to either party, any and all
shares, interests, participations, rights or other equivalents (however
designated) of corporate stock or any and all partnership or other equity
interests of such party.


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                                                                               2


            "Commission" means the United States Securities and Exchange
Commission.

            "Contract" means any contract, lease, loan agreement, mortgage,
security agreement, trust indenture, note, bond, or other agreement (whether
written or oral) or instrument.

            "Exchange Act" means the Securities Exchange Act of 1934, as
amended, and the rules and regulations of the Commission promulgated thereunder.

            "GAAP" means United States generally accepted accounting principles,
consistently applied.

            "Governmental Authority" means (i) any foreign, Federal, state or
local court or governmental or regulatory agency or authority, (ii) any
arbitration board, tribunal or mediator and (iii) with respect to any party, any
national stock exchange or Commission recognized trading market on which
securities issued by such party or any of its Subsidiaries are listed or quoted.

            "Lien" means any mortgage, pledge, lien, security interest, claim,
restriction, charge or encumbrance of any kind.

            "Person" means any individual, partnership, corporation, limited
liability company, joint venture, association, joint-stock company, trust,
unincorporated organization, government or agency or political subdivision
thereof, or other entity.

            "Registration Rights Agreement" means the Registration Rights
Agreements, dated as of the date hereof, in the forms attached hereto as
Exhibits A-1 and A-2, respectively.

            "Securities Act" means the Securities Act of 1933, as amended, and
the rules and regulations of the Commission promulgated thereunder.

            "Shares" means the Teligent Stock or the ICG Stock, as applicable.

            "subsidiary" means, with respect to any Person (i) a corporation a
majority of whose capital stock with, voting power, under ordinary
circumstances, to elect directors is at the time, directly or indirectly, owned
by such Person, by a subsidiary of such Person, or by such Person and one or
more subsidiaries of such Person, (ii) a


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partnership in which such Person or a subsidiary of such Person is, at the date
of determination, a general partner of such partnership and has the power to
direct the policies and management of such partnership or (iii) any other Person
(other than a corporation) in which such Person, a subsidiary of such Person or
such Person and one or more subsidiaries of such Person, directly or indirectly,
at the date of determination thereof, has (A) at least a majority ownership
interest or (B) the power to elect or direct the election of the directors or
other governing body of such Person.

            "Transactions" means the transactions contemplated by this
Agreement.

                                   ARTICLE II

                                SALE AND PURCHASE

            SECTION 2.1. Agreement to Sell and to Purchase. On the Closing Date,
and upon the terms and subject to the conditions set forth in this Agreement,
(i) Quadrangle shall sell to ICG, and ICG shall purchase and accept from
Quadrangle, the Teligent Stock in exchange for the ICG Stock and (ii) ICG shall
sell to Quadrangle, and Quadrangle shall purchase and accept from ICG, the ICG
Stock in exchange for the Teligent Stock (both of the foregoing sales and
purchase collectively, the "Share Exchange").

            SECTION 2.2. Closing. The closing of the Share Exchange shall take
place on a date to be specified by Quadrangle and ICG, which shall be no later
than the second Business Day after the date as of which all of the conditions
set forth in Article V hereof shall have been satisfied (or, to the extent
permitted by law, waived by the party or parties entitled to the benefit
thereof) or at such other time and date as the parties hereto shall agree in
writing (such date and time, the "Closing Date"), at the offices of O'Sullivan,
Graev & Karabell, located at 30 Rockefeller Plaza, New York, New York 10112 or
at such other place as the parties hereto shall agree in writing.

            At the Closing, (a) Quadrangle shall deliver or cause to be
delivered to ICG certificates representing the Teligent Stock, and ICG shall
deliver or cause to be delivered to Quadrangle certificates representing the ICG
Stock, which certificates shall be in definitive form and


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registered in the name of ICG or Quadrangle, as applicable, or such party's
nominee or designee and (b) each party hereto shall deliver to the other party:

            (i) an officer's certificate of such party as contemplated
      by Section 5.1(d);

            (ii) a certificate of the secretary of such party covering such
      matters as are customarily covered by such certificates, in form and
      substance reasonably acceptable to the other party; and

            (iii) a long-form good standing certificate of such party issued by
      the Secretary of State of the State of Delaware.

            SECTION 2.3. Anti-Dilution Provisions. In the event the parent of
either party changes (or establishes a record date for changing) the number of
shares of its common stock issued and outstanding prior to the Closing Date as a
result of a stock split, stock dividend, recapitalization, subdivision,
reclassification, combination, exchange of shares or similar transaction with
respect to its outstanding common stock and the record date therefor shall be
prior to the Closing Date, the number of shares to be sold hereunder by such
party and purchased by the other party shall be proportionately adjusted to
reflect such stock split, stock dividend, recapitalization, subdivision,
reclassification, combination, exchange of shares or similar transaction.

                                   ARTICLE III

                         REPRESENTATIONS AND WARRANTIES

            Quadrangle hereby represents and warrants to ICG and ICG hereby
represents and warrants to Quadrangle on the date hereof and on and as of the
Closing Date as follows:

            SECTION 3.1. Organization and Standing. Each of such party and its
subsidiaries is duly incorporated, validly existing and in good standing under
the laws of its state of incorporation and has all requisite corporate power and
authority to own its properties and assets and to carry on its business as it is
now being conducted and as proposed to be conducted. Each of such party and its
subsidiaries is duly qualified to transact business as a foreign corporation and
is in good standing in each jurisdiction in which the character of the
properties owned or leased by it or the nature of its business makes such
qualification necessary,


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except for any such failures to so qualify or be in good standing that would
not, individually or in the aggregate, reasonably be expected to have a material
adverse effect on the condition (financial or otherwise), business, assets or
results of operations of such party and its subsidiaries, taken as a whole (a
"Material Adverse Effect").

            SECTION 3.2. Capital Stock. (a) Such party is the record and
beneficial owner of, and has good and marketable title to, the Shares to be sold
by it hereunder, free and clear of any Lien. Such party has the sole right to
transfer, pledge, assign or otherwise dispose of (including by gift)
("Transfer") the Shares to be sold by such party, and none of such Shares is
subject to any voting trust or other agreement, arrangement or restrictions with
respect to the Transfer of such Shares.

            (b) Each Share to be sold by such party hereunder will be duly
authorized and validly issued and fully paid and nonassessable, and the issuance
thereof will not have been subject to any preemptive rights or made in violation
of any Applicable Law.

            SECTION 3.3. Authorization; Enforceability. Such party has the
corporate power and authority to execute, deliver and perform its obligations
under this Agreement, and has taken all action necessary to authorize the
execution, delivery and performance by it of this Agreement and the consummation
of the Share Exchange. No other corporate or stockholder action on the part of
such party is necessary for such authorization, execution, delivery and
consummation. Such party has duly executed and delivered this Agreement. This
Agreement constitutes a legal, valid and binding obligation of such party.

            SECTION 3.4. No Violation; Consents. (a) The execution, delivery and
performance by such party of this Agreement and the consummation by such party
of the Share Exchange do not and will not contravene any Applicable Law, except
for any such contravention that would not, individually or in the aggregate,
reasonably be expected to have a Material Adverse Effect. Except as set forth on
Schedule 3.4(a), the execution, delivery and performance by such party of this
Agreement and the consummation of the Share Exchange (i) will not (A) violate,
result in a breach of or constitute (with or without due notice or lapse of time
or both) a default (or give rise to any right of termination, cancelation or
acceleration) under any Contract to which such party or its parent is a party or
by which such party or its parent is bound or to which any of their assets is
subject, or (B) result in the creation or


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imposition of any Lien upon any of the assets of such party's parent, except for
any such violations, breaches, defaults or Liens that would not, individually or
in the aggregate, have a Material Adverse Effect and (ii) will not conflict with
or violate any provision of the certificate of incorporation or bylaws or other
governing documents of such party.

            (b) Except for (i) the filings by such party required by the HSR
Act, (ii) the approval of Teligent's stockholders required by Section 203(a)(3)
of the Delaware General Corporation Law (the "Stockholder Approval"), (iii)
applicable orders and permits, if any, approving the Transactions from state
regulatory authorities and (iv) applicable filings, if any, required by
applicable federal and state laws, in each case, which shall be made (or are not
required to be made) on or prior to the Closing Date, no consent, authorization
or order of, or filing or registration with, any Governmental Authority or other
Person is required to be obtained or made by such party for the execution,
delivery and performance of this Agreement or the consummation by such party of
the Share Exchange, except where the failure to obtain such consents,
authorizations or orders, or make such filings or registrations, would not,
individually or in the aggregate, reasonably be expected to have a Material
Adverse Effect or a material adverse effect on the ability of such party to
consummate the Transactions.

            SECTION 3.5. Litigation. There are not any (a) outstanding judgments
against or affecting such party or any of its subsidiaries, (b) proceedings
pending or, to the knowledge of such party, threatened against or affecting such
party or any of its subsidiaries or (c) investigations by any Governmental
Authority that are, to the knowledge of such party, pending or threatened
against or affecting such party or any of its subsidiaries that in any manner
challenge or seek to prevent, enjoin, alter or materially delay the consummation
of the Transactions.

            SECTION 3.6. Commission Filings; Financial Statements. (a) Such
party's parent has filed all reports, registration statements and other filings,
together with any amendments or supplements required to be made with respect
thereto, that it has been required to file with the Commission under the
Securities Act and the Exchange Act. As of the respective dates of their filing
with the Commission, all reports, registration statements and other filings
filed by such party's parent with the Commission together with all notes,
exhibits and schedules thereto and documents incorporated by reference therein
(the "Commission Filings") complied in all material respects with the


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applicable provisions of the Securities Act and the Exchange Act and did not
contain any untrue statement of a material fact or omit to state a material fact
required to be stated therein, or necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading.

            (b) Each of the historical consolidated financial statements of such
party's parent (including any related notes or schedules) included in the
Commission Filings was prepared in accordance with GAAP (except as may be
disclosed therein), and complied in all material respects with the rules and
regulations of the Commission. Such financial statements fairly present the
consolidated financial position of such party's parent and its subsidiaries as
of the dates thereof and the consolidated results of operations, cash flows and
changes in stockholders' equity for the periods then ended (subject, in the case
of the unaudited interim financial statements, to normal, recurring year-end
audit adjustments). Except as set forth or reflected in the Commission Filings
filed prior to the date hereof, such party's parent does not have any
liabilities or obligations of any nature (whether accrued, absolute, contingent,
unasserted or otherwise) that individually or in the aggregate would reasonably
be expected to have a Material Adverse Effect.

            SECTION 3.7. Material Adverse Change. Except as disclosed in the
Commission Filings, since September 30, 1999, there has not been any event,
occurrence or development of a state of circumstances or facts that has had, or
could have reasonably be expected to have, a Material Adverse Effect on such
party's parent.

            SECTION 3.8. Private Placement. (a) Such party understands that the
offering and sale of the Shares in the Share Exchange by the other party is
intended to be exempt from registration under the Securities Act pursuant to
Section 4(2) thereof.

            (b) Such party (either alone or together with its advisors) has
sufficient knowledge and experience in financial and business matters so as to
be capable of evaluating the merits and risks of its investment in the Shares to
be sold hereunder by the other party and is capable of bearing the economic
risks of such investment.

            (c) Such party is acquiring the Shares to be sold hereunder by the
other party for its own account (or for accounts over which it exercises
investment authority), for


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investment and not with a view to the public resale or distribution thereof in
violation of any securities law.

            (d) Such party understands that the Shares to be sold hereunder by
the other party will be issued in a transaction exempt from the registration or
qualification requirements of the Securities Act and applicable state securities
laws, and that such Shares must be held indefinitely unless a subsequent
disposition thereof is registered or qualified under the Securities Act and such
state laws or is exempt from such registration or qualification.

            (e) Such party (A) has been furnished with or has had full access to
all of the information that it considers necessary or appropriate to make an
informed investment decision with respect to the Shares to be sold hereunder by
the other party and that it has requested from the other party, (B) has had an
opportunity to discuss with management of the other party the intended business
and financial affairs of the other party and to obtain information (to the
extent the other party possessed such information or could acquire it without
unreasonable effort or expense) necessary to verify any information furnished to
it or to which it had access and (C) can bear the economic risk of (x) an
investment in the Shares to be sold hereunder by the other party indefinitely
and (y) a total loss in respect of such investment, has such knowledge and
experience in business and financial matters so as to enable it to understand
and evaluate the risks of and form an investment decision with respect to its
investment in the Shares to be sold hereunder by the other party and to protect
its own interest in connection with such investment.

                                   ARTICLE IV

                                    COVENANTS

            SECTION 4.1. Agreement to Take Necessary and Desirable Actions. Each
party shall (a) subject to the satisfaction of the conditions set forth in
Section 5.1, execute and deliver such other documents, certificates, agreements
and other writings and (b) take such other actions, in each case, as may be
necessary or reasonably requested by the other party in order to consummate the
Transactions in accordance with the terms of this Agreement.

            SECTION 4.2. Compliance with Conditions; Commercially Reasonable
Efforts. Each party shall use all commercially reasonable efforts to cause all
conditions


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precedent to the obligations of the parties hereto to be satisfied. Upon the
terms and subject to the conditions of this Agreement, each party will use all
commercially reasonable efforts to take, or cause to be taken, all action, and
to do, or cause to be done, all things necessary, proper or advisable consistent
with Applicable Law to consummate the Transactions in accordance with the terms
of this Agreement.

            SECTION 4.3. HSR Act Notification. Each party shall (a) use all
commercially reasonable efforts to file or cause to be filed, as promptly as
practicable after the execution and delivery of this Agreement, with the United
States Federal Trade Commission and the Antitrust Division of the United States
Department of Justice, all reports and other documents required to be filed by
it under the HSR Act concerning the transactions contemplated hereby and (b) use
all commercially reasonable efforts to promptly comply with or cause to be
complied with any requests by the United States Federal Trade Commission or the
Antitrust Division of the United States Department of Justice for additional
information concerning such transactions, in each case so that the waiting
period applicable to this Agreement and the transactions contemplated hereby
under the HSR Act shall expire as soon as practicable after the execution and
delivery of this Agreement. Each party agrees to request, and to cooperate with
the other party in requesting, early termination of any applicable waiting
period under the HSR Act.

            SECTION 4.4. Consents and Approvals. Each party shall use all
commercially reasonable efforts to obtain all necessary consents, waivers,
authorizations and approvals of all Governmental Authorities and of all other
Persons required in connection with the execution, delivery and performance of
this Agreement or the consummation of the Transactions.

            SECTION 4.5. Legends. So long as applicable, each certificate
representing any portion of the Shares shall be stamped or otherwise imprinted
with a legend in the following form (in addition to any legend required under
applicable state securities laws):

      "THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
      THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT") OR THE
      SECURITIES LAWS OF ANY STATE OF THE UNITED STATES. SUCH SHARES MAY NOT BE
      OFFERED, SOLD, TRANSFERRED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED OF
      IN THE ABSENCE OF SUCH


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      REGISTRATION OTHER THAN PURSUANT TO AN EXEMPTION FROM SUCH REGISTRATION
      REQUIREMENTS.

After the above requirement for a legend is no longer applicable because the
Shares are freely transferable under the Securities Act, such party shall remove
such legend upon request from a holder of such Shares, if outside counsel for
such holder reasonably determines that the transfer of such Shares is no longer
restricted by the Securities Act and outside counsel for such party reasonably
concurs in such determination.

            SECTION 4.6. Separate Business. Each party agrees to operate its
business and hold its property separate from any of its direct or indirect
parents.



                                    ARTICLE V

                         CONDITIONS PRECEDENT TO CLOSING

            SECTION 5.1. Conditions to Each Party's Obligations. The obligations
of a party hereunder required to be performed on the Closing Date shall be
subject to the satisfaction or waiver, at or prior to the Closing, of the
following conditions:

            (a) The representations and warranties of the other party contained
in this Agreement and of the other party's parent contained in the Registration
Rights Agreement (i) shall have been true and correct when made and (ii) shall
be (A) in the case of representations and warranties that are qualified as to
materiality or Material Adverse Effect, true and correct and (B) in all other
cases, true and correct in all material respects, in the case of clauses (A) and
(B), as of the Closing Date with the same force and effect as though made on and
as of the Closing Date.

            (b) The other party shall have performed in all material respects
all of its obligations, agreements and covenants contained in this Agreement and
the other party's parent shall have performed in all material respects all of
its obligations, agreements and covenants contained in the Registration Rights
Agreement to be performed and complied with at or prior to the Closing Date.

            (c) The parent of the other party shall have entered into the
Registration Rights Agreement and such agreements shall be in full force and
effect.


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            (d) The other party shall have delivered to such party a certificate
executed by it or on its behalf by a duly authorized representative, dated the
Closing Date, to the effect that each of the conditions specified in paragraphs
(a) through (c) of this Section 5.1 has been satisfied.

            (e) Any applicable waiting period under the HSR Act with respect to
the consummation of the Transactions shall have expired or been terminated.

            (f) No provision of any Applicable Law, or any injunction, order or
decree of any Governmental Entity shall be in effect which has the effect of
making the Transactions illegal or shall otherwise restrain or prohibit the
consummation of the Transactions.

            (g) All necessary orders and permits approving the Transactions from
all applicable state regulatory authorities shall have been obtained.

            (h) The Stockholder Approval shall have been obtained.

                                   ARTICLE VI

                                  MISCELLANEOUS

            SECTION 6.1. Indemnification. (a) All representations and warranties
contained in this Agreement shall survive the Closing for 18 months and all
covenants and agreements shall survive indefinitely. Notwithstanding the
foregoing, with respect to claims asserted pursuant to this Section 6.1 before
the expiration of the applicable representation or warranty such claims shall
survive until the date they are finally adjudicated or otherwise resolved.

            (b) Each party agrees to indemnify and hold harmless the other party
and each of such party's directors, officers, employees, representatives or
agents (each an "indemnified person"), from and against (and to reimburse each
indemnified person as Losses (as defined below) are incurred) any and all losses
(including, but not limited to, impairment of the value of the Shares as of the
date such loss first becomes known, but excluding consequential damages),
claims, damages, liabilities, costs and expenses (collectively, "Losses") to
which any indemnified person may become subject or which any indemnified person
may incur based upon, arising out of, or in connection with (i) a breach of any
representation, warranty or covenant of this


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Agreement by such party or (ii) any claim, litigation, investigation or
proceeding brought by or on behalf of any Person other than such party relating
to the Share Exchange, and to reimburse each indemnified person upon demand for
any reasonable legal or other reasonable out of pocket expenses incurred in
connection with investigating or defending any of the foregoing, provided the
maximum amount indemnifiable to such other party (and its successors or assigns)
under clause (i) shall not exceed the fair market value on the Closing Date of
the Shares received hereunder by such other party.

            (c) If a Person entitled to indemnity hereunder (an "Indemnified
Party") asserts that Quadrangle or ICG, as applicable (the "Indemnifying Party")
has become obligated to the Indemnified Party pursuant to Section 6.1(b), or if
any suit, action, investigation, claim or proceeding is begun, made or
instituted as a result of which the Indemnifying Party may become obligated to
the Indemnified Party hereunder, the Indemnified Party shall notify the
Indemnifying Party promptly and shall cooperate with the Indemnifying Party, at
the Indemnifying Party's expense, to the extent reasonably necessary for the
resolution of such claim or in the defense of such suit, action or proceedings,
including making available any information, documents and things in the
possession of the Indemnified Party. Notwithstanding the foregoing notice
requirement, the right to indemnification hereunder shall not be affected by any
failure to give, or delay in giving, notice unless, and only to the extent that,
the rights and remedies of the Indemnifying Party shall have been materially
prejudiced as a result of such failure or delay.

            (d) In fulfilling its obligations under this Section 6.1, after the
Indemnifying Party has provided each Indemnified Party with a written notice of
its acceptance of liability under this Section 6.1, as between such Indemnified
Party and the Indemnifying Party, the Indemnifying Party shall have the right to
investigate, defend, settle or otherwise handle, with the aforesaid cooperation,
any claim, suit, action or proceeding brought by a third party in such manner as
the Indemnifying Party may in its sole discretion reasonably deem appropriate;
provided, that (i) counsel retained by the Indemnifying Party is reasonably
satisfactory to the Indemnified Party and (ii) the Indemnifying Party will not
consent to any settlement or entry of judgment imposing any obligations on any
other party hereto other than financial obligations for which such party will be
indemnified hereunder, unless such party has consented in writing to such
settlement or judgment (which consent may be given or withheld in its sole


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discretion) and (iii) the Indemnifying Party will not consent to any settlement
or entry of judgment unless, in connection therewith, the Indemnifying Party
obtains a full and unconditional release of the Indemnified Party from all
liability with respect to such suit, action, investigation claim or proceeding.
Notwithstanding the Indemnifying Party's election to assume the defense or
investigation of such claim, action or proceeding, the Indemnified Party shall
have the right to employ separate counsel and to participate in the defense or
investigation of such claim, action or proceeding, which participation shall be
at the expense of the Indemnifying Party, if (i) on the advice of counsel to the
Indemnified Party use of counsel of the Indemnifying Party's choice could
reasonably be expected to give rise to a material conflict of interest, (ii) the
Indemnifying Party shall not have employed counsel reasonably satisfactory to
the Indemnified Party to represent the Indemnified Party within a reasonable
time after notice of the assertion of any such claim or institution of any such
action or proceeding, (iii) the Indemnifying Party shall authorize the
Indemnified Party to employ separate counsel at the Indemnifying Party's expense
or (iv) such action shall seek relief other than monetary damages against the
Indemnified Party.

            (e) The parties agree that any payment of Losses made hereunder will
be treated by the parties on their tax returns as an adjustment to the Purchase
Price. If, notwithstanding such treatment by the parties, a final determination
(which shall include the form 870-AD or successor form) with respect to the
Indemnified Party or any of its affiliates causes any such payment not to be
treated as an adjustment to Purchase Price, then the Indemnifying Party shall
indemnify the Indemnified Party for any taxes payable by the Indemnified Party
or any subsidiary by reason of the receipt of such payment (including any
payments under this 6.1(e)), determined at an assumed marginal tax rate equal to
the highest marginal tax rate then in effect for corporate taxpayers in the
relevant jurisdiction.

            SECTION 6.2. Notices. All notices, demands, requests, consents,
approvals or other communications (collectively, "Notices") required or
permitted to be given hereunder or which are given with respect to this
Agreement shall be in writing and shall be personally served, delivered by
reputable air courier service with charges prepaid, or transmitted by hand
delivery, telegram, telex or facsimile, addressed as set forth below, or to such
other address as such party shall have specified most recently by written
notice. Notice shall be deemed given on the date of service or transmission if
personally served or transmitted


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                                                                              14


by telegram, telex or facsimile. Notice otherwise sent as provided herein shall
be deemed given on the next business day following delivery of such notice to a
reputable air courier service.

            To Quadrangle:

             c/o  Teligent, Inc.
                  8065 Leesburg Pike
                  Suite 400
                  Vienna, VA 22182
                  Attn:  General Counsel
                  Telephone:  (703) 762-5100
                  Fax:  (703) 762-5227

            with a copy to:

                  Cravath, Swaine & Moore
                  Worldwide Plaza
                  825 Eighth Avenue
                  New York, New York 10019
                  Attn:  Scott A. Barshay
                  Telephone:  (212) 474-1009
                  Fax:  (212) 474-3700

            To ICG:

             c/o  ICG Communications, Inc.
                  161 Inverness Drive West
                  P.O. Box 6742
                  Englewood, CO 80155-6742
                  Attn:  General Counsel
                  Telephone:  (303) 414-4000
                  Fax:  (303) 414-8839

            with a copy to:

                  O'Sullivan, Graev & Karabell
                  30 Rockefeller Plaza, 24th Floor
                  New York, NY 10112
                  Attn:  Audrey A. Rohan
                  Telephone:  (212) 728-5591
                  Fax:  (212) 728-5950


            SECTION 6.3. Governing Law. This Agreement shall be governed by,
interpreted under, and construed in accordance with the laws of the State of New
York, regardless of the laws that might otherwise govern under applicable
principles of conflicts of law thereof.


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                                                                              15


            SECTION 6.4. Termination. (a) This Agreement may be terminated (i)
at any time prior to the Closing Date by mutual written agreement of Quadrangle
and ICG, (ii) if the Closing shall not have occurred on or prior to the later of
(A) April 30, 2000 and (B) the Business Day following the next annual or special
meeting of stockholders of Teligent (such date, the "Termination Date"), by
either Quadrangle or ICG, at any time after the Termination Date, provided that
the right to terminate this Agreement under this Section 6.4(a)(ii) shall not be
available to any party whose failure to fulfill any obligation under this
Agreement was the cause of or resulted in the failure of the Closing to occur on
or before such date, (iii) if any Governmental Authority shall have issued a
nonappealable final order, decree or ruling or taken any other action having the
effect of permanently restraining, enjoining or otherwise prohibiting the
transactions contemplated by this Agreement, by either Quadrangle or ICG or (iv)
if either Quadrangle or ICG shall have breached any of its material obligations
under this Agreement, by the non-breaching party. Any party desiring to
terminate this Agreement pursuant to clauses 6.4(a)(ii), (iii) or (iv) shall
promptly give notice of such termination to the other party.

            (b) If this Agreement is terminated, as permitted by Section 6.4(a),
such termination shall be without liability of any party (or any stockholder,
director, officer, partner, employee, agent, consultant or representative of
such party) to any other party to this Agreement; provided that if such
termination shall result from the willful (i) failure of any party to fulfill a
condition to the performance of the obligations of the other party, (ii) failure
to perform a covenant of this Agreement or (iii) breach by any party hereto of
any representation or warranty contained herein, such failing or breaching party
shall be fully liable for any and all losses (excluding consequential damages)
incurred or suffered by the other party as a result of such failure or breach.
The provisions of Sections 6.2, 6.3, this Section 6.4, Sections 6.5, 6.8, 6.10,
6.11, 6.12, 6.13, 6.14 and 6.16 shall survive any termination hereof pursuant to
Section 6.4(a).

            SECTION 6.5. Entire Agreement. This Agreement (including the
exhibits hereto) (including all agreements entered into pursuant hereto and all
certificates and instruments delivered pursuant hereto) constitutes the entire
agreement of the parties with respect to the subject matter hereof and supersede
all prior and contemporaneous agreements, representations, understandings,
negotiations and discussions between the parties, whether oral or written, with
respect to the subject matter hereof.


<PAGE>

                                                                              16


            SECTION 6.6. Modifications and Amendments. No amendment,
modification or termination of this Agreement shall be binding unless executed
in writing by Quadrangle and ICG.

            SECTION 6.7. Waivers and Extensions. Any party to this Agreement may
waive any condition, right, breach or default that such party has the right to
waive, provided that such waiver will not be effective against the waiving party
unless it is in writing, is signed by such party, and specifically refers to
this Agreement. Waivers may be made in advance or after the right waived has
arisen or the breach or default waived has occurred. Any waiver may be
conditional. No waiver of any breach of any agreement or provision herein
contained shall be deemed a waiver of any preceding or succeeding breach thereof
nor of any other agreement or provision herein contained. No waiver or extension
of time for performance of any obligations or acts shall be deemed a waiver or
extension of the time for performance of any other obligations or acts.

            SECTION 6.8. Titles and Headings. Titles and headings of sections of
this Agreement are for convenience only and shall not affect the construction of
any provision of this Agreement.

            SECTION 6.9. Exhibits and Schedules. Each of the exhibits and
schedules referred to herein and attached hereto is an integral part of this
Agreement and is incorporated herein by reference.

            SECTION 6.10. Expenses. All costs and expenses incurred in
connection with this Agreement shall be paid by the party incurring such cost or
expense.

            SECTION 6.11. Press Releases and Public Announcements. All public
announcements or disclosures relating to the Share Exchange or this Agreement
shall be made only if mutually agreed upon by Quadrangle and ICG, except to the
extent such disclosure is, in the opinion of counsel, required by law or by
regulation of any applicable national stock exchange or Commission recognized
trading market; provided that any such required disclosure shall only be made,
to the extent consistent with law and regulation of any applicable national
stock exchange or Commission recognized trading market, after consultation with
the other party.

            SECTION 6.12. Assignment; No Third Party Beneficiaries. This
Agreement and the rights, duties and obligations hereunder may not be assigned
or delegated by


<PAGE>

                                                                              17


either party without the other party's prior written consent except to an
affiliate of such party. Any assignment or delegation of rights, duties or
obligations hereunder made by either party in violation of the preceding
sentence shall be void and of no effect. This Agreement and the provisions
hereof shall be binding upon and shall inure to the benefit of each of the
parties and their respective successors and permitted assigns. This Agreement is
not intended to confer any rights or benefits on any Persons other than the
parties hereto, except as expressly set forth in Section 6.1 or this Section
6.12.

            SECTION 6.13. Severability. This Agreement shall be deemed
severable, and the invalidity or unenforceability of any term or provision
hereof shall not affect the validity or enforceability of this Agreement or of
any other term or provision hereof. Furthermore, in lieu of any such invalid or
unenforceable term or provision, the parties hereto intend that there shall be
added as a part of this Agreement a provision as similar in terms to such
invalid or unenforceable provision as may be possible and be valid and
enforceable.

            SECTION 6.14. Counterparts. This Agreement may be executed in
counterparts, each of which shall be deemed an original, but all of which taken
together shall constitute one and the same instrument.

            SECTION 6.15. Further Assurances. Each party hereto, upon the
request of the other party, shall do all such further acts and execute,
acknowledge and deliver all such further instruments and documents as may be
necessary or desirable to carry out the transactions contemplated by this
Agreement, including, such acts, instruments and documents as may be necessary
or desirable to convey and transfer to the Shares to be purchased by it
hereunder.

            SECTION 6.16. Remedies Cumulative. The remedies provided herein
shall be cumulative and shall not preclude the assertion by any party hereto of
any other rights or the seeking of any remedies against the other party hereto.

            SECTION 6.17. Specific Performance. The parties hereto agree that
the remedy at law for any breach of this Agreement may be inadequate, and that
any party by whom this Agreement is enforceable shall be entitled to specific
performance in addition to any other appropriate relief or remedy. Such party
may, in its sole discretion, apply to a court of competent jurisdiction for
specific performance or injunctive or such other relief as such court may deem
just and proper in order to enforce this Agreement, or prevent


<PAGE>

                                                                              18


any violation hereof, and, to the extent permitted by applicable law, each party
waives any objection to the imposition of such relief.


<PAGE>

                                                                              19


            IN WITNESS WHEREOF, the parties hereto have executed this Agreement
as of the date first above written.

                                    QUADRANGLE INVESTMENTS, INC.,

                                    by /s/   Cindy Tallent
                                      -------------------------
                                      Name:  Cindy Tallent
                                      Title: Vice President and Treasurer


                                    ICG TEVIS, INC.,

                                    by /s/   H. Don Teague
                                      -------------------------
                                      Name:  H. Don Teague
                                      Title: Executive Vice President,
                                             General Counsel and Secretary