<PAGE>   1
                                                                   EXHIBIT 10.16


                                AMENDED GUARANTY

         AMENDMENT TO GUARANTY ("AMENDMENT"), dated as of ___________, 2000,
made by and between HORIZON TELCOM, INC. (hereinafter called the "Guarantor"), a
corporation existing under the laws of the State of Ohio and RURAL TELEPHONE
FINANCE COOPERATIVE (hereinafter sometimes called the "Lender" and sometimes
called the "RTFC"), a South Dakota cooperative association.

         WHEREAS, Guarantor previously executed and delivered to Lender a
guaranty (the "Guaranty") dated August 29, 1997, guaranteeing certain
obligations of Guarantor's wholly-owned subsidiary, HORIZON PERSONAL
COMMUNICATIONS, INC. ("Borrower") under a loan agreement and a promissory note
(collectively the "1997 Loan Documents"), each dated August 29, 1997 and
designated OH 803-A-01, between Borrower and Lender providing for an extension
of credit in the principal amount of $23,557,965; and

         WHEREAS, the Borrower is a party to a certain Loan Agreement (the "2000
Loan Agreement") dated ___________________, 2000 by and between itself and RTFC
providing for an extension of credit as evidenced by a secured promissory note
(the "2000 Note") designated OH 803-9002 in the principal amount of $40,500,000;
and

         WHEREAS, under the terms of the 2000 Loan Agreement, the extension of
credit and advancement of funds called for in the 2000 Loan Agreement is
conditioned upon this amendment of the Guaranty;

         NOW THEREFORE, to induce Lender to make the extension of credit called
for in the 2000 Loan Agreement and the benefits derived by the Guarantor
therefrom, and in satisfaction of a material condition precedent to such
extension of credit by the Lender, the parties agree to amend the Guaranty to
read as follows:

1.       For and in consideration of loans, advances, acceptances, discounts and
         extensions of credit made by RURAL TELEPHONE FINANCE COOPERATIVE, a
         cooperative organized and existing under the laws of South Dakota
         ("RTFC" or "Lender"), to, for the account of, or on behalf of HORIZON
         PERSONAL COMMUNICATIONS, INC. a corporation organized and existing
         under the laws of Ohio ("Borrower") (the documents evidencing such
         obligations of Borrower to RTFC pursuant to (i) a loan agreement and a
         promissory note, each dated August 29, 1997; and (ii) a loan agreement
         and a promissory note, each dated ___________________, 2000 are
         hereinafter called the "Loan Documents"), the undersigned, HORIZON
         TELCOM, INC., a corporation organized and existing under the laws of
         Ohio ("Guarantor"), hereby absolutely and unconditionally guarantees to
         RTFC the punctual payment in full of an amount not to exceed the lesser
         of: (a) the aggregate principal amount of $7,852,655 (United States
         dollars) plus interest due thereon, or (b) 12.26% of Borrower's
         outstanding principal indebtedness plus interest due thereon under the
         Loan Documents, from the date hereof until the termination of the
         liability of the Guarantor hereunder as hereinafter provided, on
         account of any and all obligations, indebtedness and liability of the
         Borrower to RTFC pursuant to the Loan Documents, whether now existing
         or hereafter incurred, whether direct, indirect, or contingent, and
         whether otherwise guaranteed or secured, (such obligations,
         indebtedness and liability pursuant to the Loan Documents are
         hereinafter referred to as "Indebtedness").


<PAGE>   2

2.       The Guarantor further agrees to pay Lender its pro-rata portion
         (12.26%) of any and all costs, expenses and reasonable attorneys' fees
         paid or incurred by Lender in collecting or endeavoring to collect the
         Indebtedness of the Borrower, and all costs, expenses and reasonable
         attorneys' fees paid or incurred in enforcing or endeavoring to enforce
         this Guaranty. Notwithstanding anything to the contrary herein, the
         Guarantor shall not be liable for any expenses incurred in Lender's
         endeavoring to collect under the guaranty provided by Motorola, Inc.
         pursuant to the Loan Documents.

3.       The Lender may, at the Lender's option, proceed to enforce this
         Guaranty directly against the Guarantor (and any collateral securing
         performance of this Guaranty owned by the Guarantor) without first
         proceeding against the Borrower, any co-guarantor, or any other person
         liable for payment or performance under the Loan Documents and without
         first proceeding against or exhausting any collateral now or hereafter
         held by the Lender to secure payment or performance under the Loan
         Documents.

4.       The Guarantor waives diligence, presentment, protest, notice of
         dishonor, demand for payment, notice of nonpayment or nonperformance,
         notice of the incurrence of indebtedness by Borrower, notice of
         acceptance of this Guaranty and all other notices of any nature in
         connection with the exercise of the Lender's rights under the Loan
         Documents or this Guaranty. Performance by the Guarantor hereunder will
         not entitle the Guarantor to any payment by the Borrower under any
         claim for contribution, indemnification, subrogation or otherwise,
         until such time as all Indebtedness owing to the Lender has been paid.
         The Guarantor waives the right to require Lender to file suit against
         the Borrower or any other party before enforcing this Guaranty, and all
         rights to setoffs and counterclaims against the Lender and agrees that
         any subrogation rights which the Guarantor might now or hereafter hold
         against the Borrower and any co-guarantors will be subordinate, junior
         and inferior to all rights which the Lender might now or hereafter hold
         against the Borrower and any co-guarantors.

5.       The Guarantor hereby consents and agrees that renewals and extensions
         of time of payment, surrender, release, exchange, substitution, dealing
         with or taking of additional collateral security, taking or release of
         other guarantees, abstaining from taking advantage of or realizing upon
         any collateral security or other guarantees and any and all other
         forbearances or indulgences granted by Lender to the Borrower or any
         other party may be made, granted and effected by Lender without notice
         to the Guarantor and without in any manner affecting its liability
         hereunder.

6.       Nothing herein contained shall limit the Lender in exercising any
         rights held under any one or more of the Loan Documents. In the event
         of any default under the Loan Documents or this Guaranty, the Lender
         will be entitled to selectively and successively enforce any one or
         more of the rights held by the Lender and such action will not be
         deemed a waiver of any other rights held by the Lender. All of the
         remedies of the Lender under this Guaranty and the Loan Documents are
         cumulative and not alternative. If the Lender elects to foreclose any
         lien created by the Loan Documents, the Lender is authorized to
         purchase for the Lender's account all or any part of the collateral
         covered by such lien at public or private sale and to credit the amount
         recovered first against any portion of the Indebtedness for which the
         Guarantor is liable with any balance remaining to be applied in
         reduction of the liability of the Guarantor hereunder.

7.       In the event that a petition in bankruptcy or for an arrangement or
         reorganization of the Borrower under the bankruptcy laws or for the
         appointment of a receiver for the Borrower or any of its property is
         filed by or against the Borrower, or if the Borrower shall make an
         assignment for the


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<PAGE>   3

         benefit of creditors or shall become insolvent, all Indebtedness of the
         Borrower shall, for the purpose of this Guaranty, be deemed at Lender's
         election to have become immediately due and payable.

8.       Guarantor hereby represents and warrants that:

         a.       Good Standing. Guarantor is a corporation duly organized,
                  validly existing and in good standing under the laws of the
                  State of Ohio, has the power to own its property and to carry
                  on its business, is duly qualified to do business, and is in
                  good standing in each jurisdiction in which the transaction of
                  its business makes such qualification necessary.

         b.       Authority. Guarantor has the corporate power and authority to
                  enter into this Guaranty, to execute and deliver all documents
                  and instruments required hereunder, and to incur and perform
                  the obligations provided for herein, all of which have been
                  duly authorized by all necessary and proper corporate and
                  other action.

         c.       Other Obligations. The aggregate amount of obligations
                  guaranteed hereunder shall not exceed the maximum amount
                  allowed under any mortgage, indenture or agreement of any kind
                  entered into by or affecting the Guarantor at the time Lender
                  may seek payment under this Guaranty.

9.       Guarantor covenants and agrees with Lender that, until all of the
         obligations guaranteed hereunder shall have been satisfied in full:

         a.       Control. The Guarantor will not merge, consolidate, liquidate,
                  alter or otherwise permit alteration of control of the
                  Guarantor without the prior written consent of Lender. Control
                  shall be as defined by regulations for telephone companies
                  issued by the Federal Communications Commission.

         b.       Additional Indebtedness. The Guarantor will not borrow money
                  on a secured or unsecured basis from any other lender without
                  obtaining Lender's prior written consent. Furthermore, no
                  subsidiary of the Guarantor will borrow money on a secured or
                  unsecured basis from any other lender, or incur any additional
                  secured or unsecured Indebtedness, or enter into any Leases,
                  unless at that time Guarantor and its subsidiaries shall have
                  a consolidated Net Worth equal to or greater than forty
                  percent (40%); provided, however, Guarantor and its
                  subsidiaries may grant purchase money secured indebtedness or
                  incur unsecured trade debt or pay other current operating
                  liabilities that arise in the ordinary course of business so
                  long as the aggregate total of such debt does not exceed five
                  percent (5%) of Guarantor's consolidated total assets. If
                  Guarantor and its subsidiaries' consolidated Net Worth exceeds
                  forty percent (40%), then Guarantor's subsidiaries may incur
                  additional Guarantor's Indebtedness or enter into Leases
                  without prior written approval of Lender so long as the
                  Guarantor and its subsidiaries meet the forty percent (40%)
                  consolidated Net Worth test after incurring such additional
                  Guarantor's Indebtedness or entering into such Leases;
                  provided, further, however, Guarantor's subsidiary must give
                  at least thirty (30) days written notice to Lender prior to
                  incurring or entering into any additional Leases or term
                  loans, guarantees, lines of credit or other third-party credit
                  facilities. Notwithstanding anything to the contrary herein,
                  without Lender's prior written consent, Guarantor's
                  subsidiary, The Chillicothe Telephone Company ("Chillicothe"),
                  will be able to incur additional secured indebtedness and
                  unsecured indebtedness not to exceed ten percent (10%) of
                  Chillicothe's


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                  stand-alone total assets provided that Chillicothe: (i) meets
                  the forty percent (40%) unconsolidated Net Worth test after
                  incurring such additional indebtedness; (ii) has a current
                  assets to current liabilities ratio of 1.10 after incurring
                  such additional indebtedness; and (iii) along with Guarantor
                  are in compliance with all of their loan and guaranty
                  documents with Lender. Furthermore, Lender hereby expressly
                  acknowledges, and agrees to except from the preceding
                  calculations, Chillicothe's conversion of $4,000,000 of
                  short-term debt to long-term debt and its proposed addition of
                  $6,000,000 of long-term switch financing as presented to
                  Lender in conjunction with Borrower's proposed financing.

                  For purposes of this Guaranty, unless stated otherwise "Net
                  Worth" shall be calculated on a consolidated basis for
                  Guarantor and all its subsidiaries, and shall be calculated by
                  dividing equity (as determined by subtracting total
                  liabilities from total assets) by total assets. For purposes
                  of this Guaranty, "Leases" shall mean any lease of property by
                  which Guarantor or any of its subsidiaries shall be obligated
                  for rental or other payments which individually are in excess
                  of $50,000 per year, or in the aggregate are in excess of
                  $1,500,000 per year. For purposes of this Guaranty,
                  "Guarantor's Indebtedness" shall include all items which would
                  properly be included in the liability section of a balance
                  sheet or in a footnote to a financial statement, in accordance
                  with generally accepted accounting principles including,
                  without limitation, contingent liabilities.

          c.      Dividends and Other Cash Distributions. The Guarantor will
                  not, in any one fiscal year, without the prior approval in
                  writing of the Lender (i) declare or pay any dividends or make
                  any other distribution to its stockholders with respect to its
                  capital stock; (ii) purchase or redeem or retire any of its
                  capital stock; or (iii) pay any management fees or if already
                  paying a management fee, pay an increase in management fees
                  unless with respect to any of the foregoing (after giving
                  effect to such transaction) Guarantor's Net Worth shall exceed
                  twenty five percent (25%); provided, however, without Lender's
                  prior written consent, Guarantor may make dividend payments or
                  distributions equal to its prevailing consolidated net income
                  so long as the total amount of dividends paid by Guarantor in
                  any given fiscal year does not exceed $1,914,779.

         d.       Sale of Assets. The Guarantor and any subsidiary of the
                  Guarantor may not, without prior written approval of the
                  Lender, sell, lease or transfer any asset unless the fair
                  market value of such asset is less than 1% of Guarantor's
                  consolidated total assets and the aggregate value of assets
                  sold, leased or transferred in any 12-month period is less
                  than 5% of Guarantor's consolidated total assets.
                  Notwithstanding anything to the contrary herein, Guarantor and
                  its subsidiaries may: (i) sell securities issued or guaranteed
                  by the United States government or any agency or
                  instrumentality thereof, or securities or obligations of
                  institutions whose senior unsecured debt obligations are rated
                  by at least two nationally recognized ratings organizations in
                  either of its two highest categories; and (ii) sell, lease or
                  transfer inventory, customer premise equipment and PABX
                  equipment. Notwithstanding anything to the contrary herein,
                  Guarantor may not sell, transfer, encumber or otherwise convey
                  any of its voting Common Stock in Chillicothe.

         e.       Financial Reports and Other Information. The Guarantor will
                  furnish, in form and substance satisfactory to Lender: (a) a
                  full and complete report of Guarantor's and its subsidiaries'
                  financial condition at least once during each 12-month period
                  during the term hereof but in no event later than 120 days
                  after the end of each fiscal year of Guarantor, which shall
                  include (i) annual financial statements prepared on a
                  consolidated basis and audited by


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                  independent public accountants selected by Guarantor and
                  reasonably acceptable to Lender, accompanied by an opinion of
                  such accountants reasonably acceptable to Lender, and (ii)
                  unaudited annual consolidating financial statements of
                  Guarantor and its subsidiaries; (b) within 120 days of the
                  close of each calendar year, a written statement signed by the
                  Guarantor's president, chief executive officer or similar
                  presiding officer stating that to the best of said person's
                  knowledge that the Guarantor has fulfilled all of its
                  obligations hereunder or, if there has been a default in the
                  fulfillment of any such obligations, specifying each such
                  default known to such person and the nature and status
                  thereof; and (c) such other information, reports or statements
                  concerning the operations, business affairs and/or financial
                  condition of Guarantor and its subsidiaries as the Lender may
                  reasonably request from time to time.

         f.       Financial Books; Lender Right of Inspection: Guarantor and its
                  subsidiaries will at all times keep, and safely preserve,
                  proper books, records and accounts in which full and true
                  entries will be made of all of the dealings, business and
                  affairs of the Guarantor, in accordance with methods of
                  accounting prescribed by the state regulatory body having
                  jurisdiction over the Guarantor, or in the absence of such
                  regulatory body or such prescription, in accordance with
                  generally accepted accounting principles. The Lender, through
                  its representatives, shall at all times during reasonable
                  business hours have access to, and the right to inspect and
                  make copies of, any or all books, records and accounts, and
                  any or all invoices, contracts, leases, payrolls, canceled
                  checks, statements and other documents and papers of every
                  kind belonging to or in possession of the Guarantor and its
                  subsidiaries and pertaining to the Guarantor's and its
                  subsidiaries' property or business.

         g.       Loans, Investments and Other Obligations: (a) The Guarantor
                  will not, without first obtaining the written approval of
                  Lender: (i) purchase or make any commitment to purchase any
                  stock, bonds, notes, debentures or other securities or
                  obligations of or beneficial interests in, (ii) make any other
                  investments in, (iii) make any loan to, or (iv) guarantee,
                  assume, or otherwise become liable for any obligation of, any
                  corporation, association, partnership, joint venture, trust,
                  government or any agency or department thereof, or any other
                  entity of any kind if the aggregate amount of all such
                  purchases, investments, loans and guarantees exceeds the
                  greater of ten percent (10%) of Total Plant or thirty percent
                  (30%) of Net Worth. For purposes of this Guaranty, "Total
                  Plant" shall be calculated on a consolidated basis for the
                  Guarantor and all its subsidiaries and shall mean the total of
                  all assets included in property, plant and equipment pursuant
                  to generally accepted accounting principles and shall exclude
                  any goodwill or plant acquisition adjustments. (b) The
                  following shall not be included in the limitation on
                  purchases, investments, loans and guarantees in (a) above: (i)
                  bonds, notes, debentures, stock, or other securities or
                  obligations issued by or guaranteed by the United States
                  government or any agency or instrumentality thereof; (ii)
                  bonds, notes, debentures, stock, commercial paper,
                  subordinated capital certificates, or any other security or
                  obligation of institutions whose senior unsecured debt
                  obligations are rated by at least two nationally recognized
                  rating organizations in either of its two highest categories;
                  (iii) investments incidental to loans made by RTFC; (iv) any
                  deposit that is fully insured by the Federal Government; and
                  (v) common stock or other equity investments in Borrower. For
                  purposes of this section, securities and investments shall be
                  calculated at cost and exclude any cash surrender value of
                  life insurance.

10.      If the Guarantor fails to make any payment pursuant to Lender's demand
         for payments provided for in Sections 1 and 2 hereunder, then a
         "Payment Event of Default" shall have been deemed to occur


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<PAGE>   6

         hereunder and then Lender may, upon five (5) days written notice (with
         a copy of such notice to Borrower) during which time Guarantor or
         Borrower shall have the right to cure such Payment Event of Default, in
         addition to any other rights available to Lender at law or in equity,
         declare the maximum amount guaranteed by Guarantor at such time
         pursuant to Sections 1 and 2 hereunder to be immediately due and
         payable without presentment, demand, protest or notice of any kind, all
         of which are hereby expressly waived. Any funds collected hereunder
         shall be immediately applied as a prepayment (subject to any applicable
         prepayment fees) pro-ratably to all of Borrower's Indebtedness.

11.      If the Guarantor fails to observe or perform any warranty, covenant or
         condition under Section 9 of this Guaranty, then a "Covenant Event of
         Default" shall have been deemed to occur hereunder. Upon the occurrence
         of a Covenant Event of Default, the Lender may provide written notice
         to Guarantor (with a copy of such notice to Borrower) of the occurrence
         of said Covenant Event of Default and demand that such Covenant Event
         of Default be cured within thirty (30) days of receipt of such notice.
         If such Covenant Event of Default is not cured by Guarantor, or a
         substitute guarantor is not approved in writing by Lender within such
         thirty (30) day cure period, then Lender may, in addition to any other
         rights available to Lender at law or in equity, declare a "Payment
         Event of Default" and, upon five (5) days written notice (with a copy
         of such notice to Borrower) during which time Guarantor or Borrower
         shall have the right to cure such Payment Event of Default, so declare
         the maximum amount guaranteed by Guarantor at such time pursuant to
         Sections 1 and 2 hereunder to be immediately due and payable without
         presentment, demand, protest or notice of any kind, all of which are
         hereby expressly waived. Any funds collected hereunder shall be
         immediately applied as a prepayment (subject to any applicable
         prepayment fees) pro-ratably to all of Borrower's Indebtedness.

12.      If any provision of this Guaranty is held to be invalid, illegal or
         unenforceable in any respect or application for any reason, such
         invalidity, illegality or unenforceability will not affect any other
         provisions herein contained and such other provisions will remain in
         full force and effect.

13.      If any payment or thing of value should be received and accepted by the
         Lender in payment of any Indebtedness or obligation of the Borrower
         under any of the Loan Documents and it should subsequently be
         determined or adjudged that such payment be void or voidable under any
         law or statute now or hereafter in effect the receipt of such payment
         by the Lender shall, as to the Guarantor, be deemed a provisional
         receipt and if any such payment should be avoided or set aside under
         any such law or statute the Guarantor shall be and remain liable to the
         Lender in respect thereof as if such payment had not been received by
         the Lender notwithstanding any release or discharge of this Guaranty to
         the Guarantor issued or granted by the Lender in the belief or
         assumption that its receipt of such payment was absolute and not
         subject to any avoidance.

14.      THIS GUARANTY WILL BE CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
         COMMONWEALTH OF VIRGINIA. GUARANTOR HEREBY SUBMITS TO THE NONEXCLUSIVE
         JURISDICTION OF THE COURTS OF THE UNITED STATES COURTS LOCATED IN THE
         COMMONWEALTH OF VIRGINIA FOR PURPOSES OF ALL LEGAL PROCEEDINGS ARISING
         OUT OF OR RELATING TO THIS GUARANTY OR THE TRANSACTIONS CONTEMPLATED
         HEREBY. GUARANTOR IRREVOCABLY WAIVES TO THE FULLEST EXTENT PERMITTED BY
         APPLICABLE LAW, ANY OBJECTION THAT IT MAY NOW OR HEREAFTER HAVE TO THE
         ESTABLISHING OF THE VENUE OF ANY SUCH PROCEEDING BROUGHT IN SUCH A
         COURT AND ANY CLAIM THAT ANY SUCH PROCEEDING HAS BEEN BROUGHT IN AN
         INCONVENIENT FORUM. EACH OF THE


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         GUARANTOR AND THE LENDER HEREBY IRREVOCABLY WAIVES, TO THE FULLEST
         EXTENT PERMITTED BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY
         IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATING TO THIS GUARANTY OR
         THE TRANSACTIONS CONTEMPLATED HEREBY.

15.      This Guaranty shall be binding upon the Guarantor and its successors
         and assigns, and shall inure to the benefit of RTFC and its successors
         and assigns. This Guaranty may be transferred or assigned by Guarantor
         to another entity of equal or greater credit quality than Guarantor so
         long as RTFC provides its prior written consent to such transfer or
         assignment, which consent shall not be unreasonably withheld.

16.      All accounting terms not specifically defined herein shall have the
         meaning assigned to them by generally accepted accounting principles.

17.      This Guaranty shall operate as a continuing guaranty and shall expire
         only upon the satisfaction by Borrower, Guarantor, or any co-guarantor
         of all obligations owed by Borrower to RTFC under the Loan Documents.

18.      On or prior to the initial advance under the 2000 Loan Agreement to
         Borrower, Guarantor covenants to enter into revised firm equity
         subscription agreements with Borrower, in form and substance reasonably
         satisfactory to Lender, that provide for additional common equity
         capital contributions from Guarantor in the minimum amounts set forth
         below opposite the corresponding date.

<TABLE>
<CAPTION>

                    -------------------------------------------
                                Date              Amount
                    -------------------------------------------
                          <S>                   <C>
                             At closing         $15,106,203
                    -------------------------------------------
                          December 31, 2000      1,500,000
                    -------------------------------------------
                          December 31, 2001      1,000,000
                    -------------------------------------------
                          December 31, 2002      1,000,000
                    -------------------------------------------
</TABLE>

         The revised equity subscription agreement shall also provide that it
         may not be modified, transferred, or terminated by either party without
         Lender's prior written consent and the Lender shall be named as a third
         party beneficiary with regard to enforcing payments under that
         agreement.

19.      On or prior to the date of the initial advance under the 2000 Loan
         Documents to Borrower, Guarantor covenants to enter into a tax sharing
         arrangement with Borrower, in form and substance satisfactory to
         Lender, that provides for the pass through to Borrower of tax benefits
         as cash payments equal to the lesser of (i) the amounts set forth below
         opposite the corresponding date, or (ii) a positive dollar amount
         equivalent to 34% of the Borrower's book net loss.
<TABLE>
<CAPTION>

                    -------------------------------------------
                                Date                Amount
                    -------------------------------------------
                          <S>                   <C>
                          December 31, 2000     $ 4,522,000
                    -------------------------------------------
                          December 31, 2001     $ 4,619,000
                    -------------------------------------------
                          December 31, 2002     $ 1,196,000
                    -------------------------------------------
</TABLE>

         To the extent that Borrower and/or Guarantor do not have final net
         income calculations by December 31st of any given year, such parties
         shall use their best efforts to provide an estimated cash payment in
         accordance with the above schedule by December 31st of said year;
         thereafter,


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<PAGE>   8

         based on the latest available tax information but in no event later
         than March 31st of the following year, a "true-up" calculation shall be
         made whereby Guarantor shall provide Borrower an additional cash
         payment in accordance with the above schedule (if the December 31st
         contribution was underestimated) or Borrower at Guarantor's option
         shall provide Guarantor a refund payment (if the December 31st
         contribution was overestimated). Notwithstanding the timing of any
         true-ups and whenever the years final tax return is filed, Guarantor
         shall continue to be liable for any necessary payments in accordance
         with the above schedule.

         The revised tax sharing agreement shall also provide that it may not be
         modified, transferred, or terminated by either party without Lender's
         prior written consent and the Lender shall be named as a third party
         beneficiary with regard to enforcing payments under that agreement.

20.      The Guarantor hereby states, and RTFC hereby expressly acknowledges,
         that this Guaranty is not collateralized by either the stock or the
         assets of Guarantor's wholly-owned subsidiary, The Chillicothe
         Telephone Company.

21.      Whenever prior approval or consent is required under the terms and
         conditions of this Guaranty, RTFC agrees to not unreasonably withhold
         or delay such approval or consent.


IN WITNESS WHEREOF, this Guaranty has been executed and delivered by RTFC and
the undersigned Guarantor as of the _______ day of __________________, 2000.


                                        HORIZON TELCOM, INC.

(SEAL)                                  By:
                                           -------------------------------------
                                        Title:
                                              ----------------------------------
                                        Address:  68 East Main Street
                                                  Chillicothe, OH 45601
                                        Fax:      (614) 774-3400


Attest:
       -------------------------
               (Secretary)


                                        RURAL TELEPHONE FINANCE
                                        COOPERATIVE

(SEAL)                                  By:
                                           -------------------------------------
                                        Title:
                                              ----------------------------------

                                        Address:  Woodland Park
                                                  2201 Cooperative Way
                                                  Herndon, Virginia  20171-3025
                                        Fax:      (703) 709-6776
Attest:
       --------------------------
               (Secretary)


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