<PAGE>

                                                                  EXHIBIT 10.7.3

                 Fourth Amendment to the Employment Agreement


This Fourth Amendment dated September 15, 1999 is made between Madison River
Telephone Company, LLC ("Holdings") and Donald K. Roberton, ("Executive")
pursuant to paragraph 11 of that certain agreement for employment between
Holdings and Executive dated August 1, 1996 ("Employment Agreement").

Section 5.1 and 5.3(b) of the Employment Agreement shall be amended by replacing
said sections with the following:

5.1  Purchase Rights; Vesting.
     ------------------------
(a)  As of the date hereof, Executive shall have the right to purchase at any
time from Holdings Class B equity of Holdings equal to 10% of the total Class B
equity  of Holdings for an aggregate purchase price of $1,000 and Class C equity
of Holdings equal to 11.50% of the total Class C equity of Holdings for an
aggregate purchase price of $1,150.  Hereafter, Class B and Class C equity
collectively shall be referred to as "Incentive Equity").  Within 30 days after
each time that Executive exercises its right to purchase Incentive Equity, the
Executive will make an effective election with the Internal Revenue Service
under Section 83(b) of the Internal Revenue Code and the regulations promulgated
thereunder.  The parties hereto agree that the fair market value of the
Incentive Equity allocated to Executive as of the initial Employment Agreement
date for Class B is $1,000 and as of the Gulf Closing Date for Class C and for a
period of at least five business days thereafter is $1,150 and that parties
shall use such value for all Federal income tax purposes.

(b)  Twenty percent (20%) of Executive's Incentive Equity will vest on the First
Acquisition Closing Date and, provided that (except in the case of vesting
pursuant to Section 5.3(a)) Executive is still employed by Holdings, the
remainder on a daily basis over a four-year period beginning with the First
Acquisition Closing Date and ending with the Closing Date  for Gulf Coast
Services, Inc.  ("Gulf Closing Date") and any unvested remainder after the Gulf
Closing Date shall vest on a daily basis over a new four-year period beginning
with the Gulf Closing Date.  All unvested Incentive Equity will become fully
vested immediately prior to the occurrence of a Liquidity Event.  "Liquidity
Event" means (i) any sale of all or substantially all of the assets of Holdings
on a consolidated basis in one transaction or series of related transactions
(but excluding sales to affiliates) for cash or marketable securities, (ii) any
sale of 50% or more of the Investor Equity (as defined in the LOI) in one
transaction or series of related transactions (but excluding sales to affiliates
and, with respect to individuals, related persons) for cash or marketable
securities or (iii) a merger, share exchange or similar transaction which
accomplishes one of the foregoing.


          5.3  Repurchase.
               ----------

(b)  Executive's vested Incentive Equity will not be subject to repurchase in
whole or in part by Holdings.
<PAGE>

     All other provisions of the Employment Agreement remain in full force and
effect.


IN WITNESS WHEREOF, Executive and Holdings have caused this Fourth Amendment to
the Employment Agreement to be executed as of the date first written above.


                              Madison River Telephone Company, LLC


                              by:     PAUL H. SUNU
                                 ----------------------------------



                                       DONALD K. ROBERTON
                                 -----------------------------------
                                 Executive