Document:

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                                 EXHIBIT 10.52

Letter of Understanding, dated December 15, 1999, from ICG Communications, Inc.,
 regarding Section 4 of the Employment Agreement between ICG Communications,
 Inc. and Douglas I. Falk.

<PAGE>

                                                   December 15, 1999

Douglas Falk
161 Inverness Drive West
Englewood, Colorado 80112

Dear Doug:

         This letter evidences our understanding that, if the Company terminates
your employment pursuant to Section 4 of the Employment Agreement between you
and the Company dated June 1, 1999, all options to purchase shares of the
Company that have been granted to you pursuant to the Company's Stock Option
Plans, but not yet vested, will immediately vest on the date of such termination
and you will be entitled to exercise all options held by you for a period of six
months after the date of termination in accordance with the plans and agreements
relating to such options.

                                                        ICG COMMUNICATIONS, INC.

                                                        By:  /s/ Don Teague
                                                             -------------------<PAGE>

                                 EXHIBIT 10.53

      Employment Agreement, dated as of July 1, 1999, by and between ICG
                   Communications, Inc. and Carla J. Wolin.
<PAGE>

                             EMPLOYMENT AGREEMENT

     THIS EMPLOYMENT AGREEMENT ("Agreement") is made as of the 1st day of July,
1999 by and between ICG Communications, Inc. ("Employer" or the "Company") and
Carla J. Wolin ("Employee").

                                R E C I T A L S

     WHEREAS, the Company desires to employ Employee as provided herein; and

     WHEREAS, Employee desires to be employed by Employer as provided herein.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein, the parties agree as follows:

     1.   Employment. The Company agrees to employ Employee and Employee hereby
          ----------
agrees to be employed on a full-time basis by the Company or by such of its
subsidiary or affiliate corporations as determined by the Company in such
position as is designated by the Company, for the period and upon the terms and
conditions hereinafter set forth.

     2.   Duties. During her employment, Employee shall perform the duties and
          ------
bear the responsibilities commensurate with her position and shall serve the
Employer faithfully and to the best of her ability. Employee shall devote 100%
of her working time to carrying out her obligations hereunder.

     3.   Compensation and Benefits.
          -------------------------

          3.1  The Company shall pay Employee during the Term of this Agreement
an annual base salary, payable semi-monthly. The annual base salary will
initially be One Hundred Forty-Five Thousand and 00/100 Dollars ($145,000.00).

          3.2  In addition to the base salary, Employee will be eligible for an
annual performance bonus in an exact amount to be determined by the Board of
Directors of the Company or the Compensation Committee of the Board. The annual
bonus will be determined in accordance with the bonus plan of the Company and
will be based on objectives and goals set for the Company and the Employee.
Employee's annual bonus is initially established at 30% of annual base salary if
all objectives and goals are met.

          3.3  In addition to salary and bonus payments as provided above, the
Company will provide Employee, during the Term of this Agreement, with the
benefits of such insurance plans, hospitalization plans and other benefits as
shall be generally provided to employees of the Company at her level and for
which Employee may be eligible under the terms and conditions thereof.

          3.4  Throughout the Term of this Agreement, the Company will reimburse
Employee for all reasonable out-of-pocket expenses incurred by Employee in
connection with the business of the Company and the performance of her duties
under this Agreement, upon presentation to the Company by Employee of an
itemized accounting of such expenses with reasonable supporting data.

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          3.5  The Company may from time to time provide to Employee stock
options pursuant to and subject to the terms and conditions of the Company's
Stock Option Plans.

     4.   Term. The initial term of this Agreement will be for one (1) year
          ----
commencing as of the date hereof ("Term"). From the date hereof, this Agreement
automatically renews from month-to-month such that there will always be one (1)
year remaining in the Term, unless and until either party shall give at least
sixty (60) days notice to the other of her or its desire to terminate this
Agreement (in such case, the Term shall end upon the date indicated in such
notice). The applicable provisions of Sections 6, 7, and 8 shall remain in full
force and effect for the time periods specified in such Sections notwithstanding
the termination of this Agreement.

     5.   Termination.
          -----------

          5.1  If Employee dies during the Term of this Agreement, this
Agreement will terminate. The Company will pay the estate of Employee an amount
equal to three months salary. In addition, the estate of Employee will be
entitled to exercise all options theretofore vested under the Company's Stock
Option Plans for a period of one (1) year after the date of death of Employee in
accordance with the plans and agreements relating to such options.

          5.2  If, during the Term of this Agreement, Employee is prevented from
performing her duties by reason of illness or incapacity for one hundred forty
(140) days in any one hundred eighty (180) day period, the Company may terminate
this Agreement, upon thirty (30) days notice to Employee or her duly appointed
legal representative. Employee will be entitled to all benefits provided under
any disability plans of the Company. In addition, Employee or her duly appointed
legal representative will be entitled to exercise all options theretofore vested
under the Company's Stock Option Plans for a period of one (1) year after the
date of termination in accordance with the plans and agreements relating to such
options.

          5.3  For the purposes of this Agreement, a "Change in Control" of the
Company shall mean and be deemed to have occurred if (a) any "person" (as such
term is used in Sections 13(d) and 14(d) of the Securities Exchange Act of 1934
as amended (Exchange Act)) is or becomes the "beneficial owner" (as defined in
Rule 13d-3 under the Exchange Act), directly or indirectly, of securities of the
Company representing 50% or more of the combined voting power of the Company's
then outstanding securities; (b) at any time a majority of the directors of the
Company are persons who were not nominated for election by the Board; (c) the
stockholders of the Company approve a merger or consolidation of the Company
with any other corporation, other than a merger or consolidation which would
result in the voting securities of the Company outstanding immediately prior
thereto continuing to represent (either by remaining outstanding or by being
converted into voting securities of the surviving entity) at least 50% of the
combined voting power of the voting securities of the Company or such surviving
entity outstanding immediately after such merger or consolidation; (d) the
Company shall sell or otherwise dispose of, in one transaction or a series of
related transactions, assets aggregating more than 50% of the assets of the
Company and its subsidiaries consolidated; or (e) the stockholders of the
Company approve a plan of complete liquidation of the Company or any agreement
for the sale or disposition by the Company of all or substantially all the
Company's assets. Upon the occurrence of a Change in Control, the Company shall
pay Employee an amount equal to one-half of the aggregate amount of her annual
base salary plus her targeted annual bonus. At the time of the occurrence of a
Change in Control all options to purchase shares of the Company that have been
granted to Employee pursuant to the Company's Stock Option Plans, but not yet
vested, will immediately vest and Employee shall be entitled to exercise such
options in accordance with the plans and agreements relating to such options. In
addition, the Company or Employee may terminate this Agreement upon at least
thirty (30) days notice at any time within one (1) year after the occurrence of
a Change in Control of the Company.

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          5.4   Employee may terminate this Agreement upon at least thirty (30)
days notice upon the occurrence of a constructive dismissal of Employee. For the
purposes of this Agreement, "constructive dismissal" shall mean, unless
consented to by Employee in writing, any of the following actions by the
Company:

          (i)   any reduction in the annual salary of Employee;

          (ii)  prior to the occurrence of a Change in Control of the Company,
                any requirement to relocate to another state or country,
                provided, however, that this provision shall not be applicable
                if the principal executive offices of the Company are being
                relocated to such state or country; and

          (iii) any material reduction in the value of Employee's benefits plans
                and programs.

          5.5   The Company may terminate this Agreement immediately for gross
negligence, intentional misconduct or the commission of a felony by the
Employee, in which case all rights under this Agreement shall end as of the date
of such termination.

          5.6   If this Agreement is terminated by the Company under Section 4,
the Company shall pay Employee a termination fee in an amount equal to the
aggregate amount of her annual base salary that would have been paid during the
remaining Term of the Agreement. If this Agreement is terminated by the Company
under Section 5.3, the Company shall pay Employee a termination fee in an amount
equal to the aggregate amount of her annual base salary plus her targeted annual
bonus. Such termination fee will be paid in a lump sum within fifteen (15) days
from the date of termination. If this Agreement is terminated by Employee under
Section 5.4, the Company will pay Employee a termination fee equal to the
aggregate amount of her annual base salary plus her targeted annual bonus. Such
termination fee will be paid in a lump sum within fifteen (15) days from the
date of termination. In addition, if Employee terminates this Agreement under
Section 5.3 or Section 5.4, all options to purchase shares of the Company that
have been granted to Employee pursuant to the Company's Stock Option Plans, but
not yet vested, will immediately vest on the date of termination and Employee
will be entitled to exercise all options held by the Employee for a period of
six (6) months after the date of termination in accordance with the plans and
agreements relating to such options.

     6.   Non-Compete and Non-Interference.
          --------------------------------

          6.1   During the Term of this Agreement, if Employee's employment with
the Company is terminated under Section 4 or Section 5.3, for a period of twelve
(12) months after such termination, Employee shall not, directly or indirectly,
own, manage, operate, control, be employed by, or participate in the ownership,
management, operation or control, of a business that is engaged in the same
business as the Company within any area constituting, during the term of
Employee's employment or at the time the Employee's employment is terminated, a
Relevant Area. A "Relevant Area" shall be defined for the purposes of this
Agreement as any area located within, or within fifth (50) miles of, the legal
boundaries or limits of any city within which the Company is engaged in business
or in which the Company has publicly announced or privately disclosed to
employee that it plans to engage in business.

                                       3
<PAGE>

          6.2  During the Term of this Agreement and for a period of twelve (12)
months after termination of this Agreement, Employee shall not (i) directly or
indirectly cause or attempt to cause any employee of the Company or any of its
affiliates to leave the employ of the Company or any affiliate, (ii) in any way
interfere with the relationship between the Company and any employee or between
an affiliate and any employee of the affiliate, or (iii) interfere or attempt to
interfere with any transaction in which the Company or any of its affiliates was
involved during the Term of this Agreement.

          6.3  Employee agrees that, because of the nature and sensitivity of
the information to which she will be privy and because of the nature and scope
of the Company's business, the restrictions contained in this Section 6 are fair
and reasonable.

     7.   Confidential Information.
          ------------------------

          7.1  The relationship between the Company and Employee is one of
confidence and trust. This relationship and the rights granted and duties
imposed by this Section shall continue until a date ten (10) years from the date
Employee's employment is terminated.

          7.2  As used in this Agreement (i) "Confidential Information" means
information disclosed to or acquired by Employee about the Company's plans,
products, processes and services, including information relating to research,
development, inventions, manufacturing, purchasing, accounting, engineering,
marketing, merchandising, selling, pricing, tariffed or contractual terms,
customer lists and prospect lists and other market information, with respect to
any of the Company's business activities; and (ii) "Inventions" means any
inventions, discoveries, concepts and ideas, whether patentable or not,
including, without limitation, processes, methods, formulas, and techniques (as
well as related improvements and knowledge) that are based on or related to
Confidential Information, that pertain in any manner to the Company's
technology, expertise or business and that are made or conceived by Employee,
either solely or jointly with others, and while employed by the Company or
within six (6) months thereafter, whether or not made or conceived during
working hours or with the use of the Company's facilities, materials or
personnel.

          7.3  Employee agrees that she shall at no time during the Term of this
Agreement or at any time thereafter disclose any Confidential Information to any
person, firm or corporation to any extent or for any reason or purpose or use
any Confidential Information for any purpose other than the conduct of the
Company's business.

          7.4  Any Confidential Information that is directly or indirectly
originated, developed or perfected to any degree by Employee during the term of
her employment by the Company shall be and remain the sole property of the
Company and shall be deemed trade secrets of the Company.

          7.5  Upon termination of Employee's employment pursuant to any of the
provisions herein, Employee or her legal representative shall deliver to the
Company all originals and all duplicates and/or copies of all documents,
records, notebooks, and similar repositories of or containing Confidential
Information then in her possession, whether prepared by her or not.

          7.6  Employee agrees that the covenants and agreements contained in
this Section 7 are fair and reasonable and that no waiver or modification of
this Section or any covenant or condition set forth herein shall be valid unless
set forth in writing and duly executed by the parties hereto.

                                       4
<PAGE>

     8.   Injunctive Relief. Upon a material breach or threatened material
          -----------------
breach by Employee of any of the provisions of Sections 6 or 7 of this
Agreement, the Company shall be entitled to an injunction restraining Employee
from such breach. Nothing herein shall be construed as prohibiting the Company
from pursuing any other remedies for such breach or threatened breach, including
recovery of damages from Employee.

     9.   No Waiver. A waiver by the Company of a breach of any provision of
          ---------
this Agreement by Employee shall not operate or be construed as a waiver of any
subsequent or other breach by Employee.

     10.  Severability. It is the desire and intent of the parties that the
          ------------
provisions of this Agreement shall be enforced to the fullest extent permissible
under the laws and public policies applied in each jurisdiction in which
enforcement is sought. Accordingly, if any particular provision or portion of
this Agreement shall be adjudicated to be invalid or unenforceable, this
Agreement shall be deemed amended to delete therefrom the portion thus
adjudicated to be invalid or unenforceable, such deletion to apply only with
respect to the operation of such provision in the particular jurisdiction in
which such adjudication is made.

     11.  Notices. All communications, requests, consents and other notices
          -------
provided for in this Agreement shall be in writing and shall be deemed given if
delivered by hand or mailed by first class mail, postage prepaid, to the last
known address of the recipient.

     12.  Governing Law. This Agreement shall be governed by and construed and
          -------------
enforced in accordance with the laws of the State of Colorado.

     13.  Assignment. Neither this Agreement nor any rights or duties hereunder
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may be assigned by Employee or the Company without the prior written consent of
the other, such consent not to be unreasonably withheld.

     14.  Amendments. No provision of this Agreement shall be altered, amended,
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revoked or waived except by an instrument in writing, signed by each party to
this Agreement.

     15.  Binding Effect. Except as otherwise provided herein, this Agreement
          --------------
shall be binding upon and shall inure to the benefit of the parties hereto and
their respective legal representatives, heirs, successors and assigns.

     16.  Execution in Counterparts. This Agreement may be executed in any
          -------------------------
number of counterparts, each of which shall be deemed an original, but all of
which together shall constitute one and the same instrument.

     17.  Entire Agreement. This Agreement sets forth the entire agreement and
          ----------------
understanding of the parties and supersedes all prior understandings, agreements
or representations by or between the parties, whether written or oral, which
relate in any way to the subject matter hereof.

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<PAGE>

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

                                            /s/ Carla J. Wolin
                                            ------------------------------------
                                            CARLA J. WOLIN

                                            ICG COMMUNICATIONS, INC.

                                            By: /s/ Don Teague
                                               ---------------------------------

                                            Name: H. Don Teague
                                                 -------------------------------

                                            Title: Executive Vice President,
                                                  ------------------------------
                                                   General Counsel, Secretary

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