Document:

<PAGE>

                                                                   Exhibit 4.8.1

                               FIRST AMENDMENT TO
                         REGISTRATION RIGHTS AGREEMENT

          THIS FIRST AMENDMENT TO REGISTRATION RIGHTS AGREEMENT (this
"Amendment") dated as of April 20, 2000 (the "Effective Date"), by and among
NETTEL COMMUNICATIONS, INC., a Delaware corporation (the "Company"), JAMES F.
KENEFICK ("Kenefick"), GOLD & APPEL TRANSFER, S.A. ("G&A") and WILLIAMS
COMMUNICATIONS, INC., a Delaware corporation ("Williams," and together with
Kenefick and G&A, the "Existing Stockholders"), those certain persons and
entities listed as a Series B Purchaser on Schedule 1 of this Amendment, (each a
                                           ----------
"Series B Purchaser" and collectively, the "Series B Purchasers") and those
certain persons and entities listed as a Series C Purchaser on Schedule 1 of
                                                               ----------
this Amendment (each a "Series C Purchaser," collectively, the "Series C
Purchasers" and together with the Series B Purchasers, the "Purchasers").

          WHEREAS, the Company entered into that certain Securities Purchase
Agreement by and among the Company and certain of the Series B Purchasers (the
"Series B Purchase Agreement"), dated as of July 23, 1999 and amended on August
2, 1999, which provided for the issuance of shares of the Company's Series B
Convertible Preferred Stock (the "Series B");

          WHEREAS, the Company entered into that certain Registration Rights
Agreement by and among the Company, the Existing Stockholders and the Series B
Purchasers (the "Registration Rights Agreement"), dated as of July 23, 1999 and
amended on August 2, 1999;

          WHEREAS, the Company is simultaneously entering into the Securities
Purchase Agreement dated as of the Effective Date by and among the Company and
the Series C Purchasers (as amended from time to time, the "Series C Purchase
Agreement"), which provides for the Company's issuance of shares of the
Company's Series C Convertible Preferred Stock (the "Series C," and together
with the Series B, the "Preferred Stock");

          WHEREAS, as an inducement to the Series C Purchasers to enter into the
Series C Purchase Agreement, the Company agreed to provide to the Series C
Purchasers certain registration rights with respect to the Common Stock of the
Company which may be acquired by the conversion of the Preferred Stock subject
to the terms and conditions of the Registration Rights Agreement;

          WHEREAS, the parties desire to amend the Registration Rights Agreement
to include the Series C  and the Series C Purchasers;

          WHEREAS, Section 2.2 of the Registration Rights Agreement provides for
amendments in a writing signed by the Company and the Required Holders; and

          WHEREAS, capitalized terms used herein without definition shall have
the meanings given to such terms in the Registration Rights Agreement.

          NOW, THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the parties hereto agree as follows:

                                       1
<PAGE>

1.  The definitions of the Registration Rights Agreement hereby shall be amended
as follows:

(a)  "Preferred Stock" shall have the meaning ascribed to such term in this
     Amendment.

(b)  "Purchaser" and "Purchasers" shall have the meanings ascribed to such terms
     in this Amendment.

2.  Schedule I of the Registration Rights Agreement is hereby deleted in its
    ----------
entirety and replaced with Schedule I to this Amendment.
                           ----------

3.  Except as otherwise provided in this Amendment, the Registration Rights
Agreement remains unchanged and in full force and effect, and references to the
"Agreement" contained in the Registration Rights Agreement shall for all
purposes be deemed to refer to the Registration Agreement as amended by this
Amendment.

4.  The Registration Rights Agreement, as amended herein, constitutes the entire
understanding and agreement among the parties hereto with respect to the subject
matter hereof, and supersedes all prior and contemporaneous agreements and
understandings, inducements or conditions, express or implied, oral or written,
among the parties hereto except as herein and therein contained.

5.  This Amendment may be executed in counterparts, each of which shall be
deemed an original, but all of which together shall constitute one and the same
instrument, and a facsimile signature shall be deemed and original.

                           [Signature page follows.]

                                       2
<PAGE>

     IN WITNESS WHEREOF, the undersigned have executed this First Amendment to
Registration Rights Agreement as of the date set forth on the first page hereof.

                              COMPANY:

                              NETTEL COMMUNICATIONS, INC.

                              By: /s/ James F. Kenefick
                                 --------------------------
                              Name: James F. Kenefick
                              Title: CEO

                              EXISTING STOCKHOLDERS:

                              /s/ James F. Kenefick
                              _____________________________________
                              James F. Kenefick

                              WILLIAMS COMMUNICATIONS, INC.

                              By: /s/ Gordon C. Martin, Jr.
                                 --------------------------
                              Name: Gordon C. Martin, Jr.
                              Title: SVP, Global Network Svcs.

                              GOLD & APPEL TRANSFER, S.A.

                              By: /s/ Walt Anderson
                                 --------------------------
                              Name: Walt Anderson
                              Title: Attorney-in-Fact

                                       3
<PAGE>

                              SERIES B PURCHASERS:

                              GOLD & APPEL TRANSFER, S.A.

                              By: /s/ Walt Anderson
                                 --------------------------
                              Name: Walt Anderson
                              Title: Attorney-in-Fact

                              NORTEL NETWORKS INC.

                              By: /s/ Mitchell L. Stone
                                 --------------------------
                              Name: Mitchell L. Stone
                              Title: Director

                              ALLIED CAPITAL CORPORATION

                              By: /s/ Scott S. Binder
                                 --------------------------
                              Name: Scott S. Binder
                              Title: Principal

                                       4
<PAGE>

                              SERIES C PURCHASERS:

                              ALLIED CAPITAL CORPORATION

                              By: /s/ Scott S. Binder
                                 --------------------------
                              Name: Scott S. Binder
                              Title: Principal

                              FOUNDATION FOR THE INTERNATIONAL NON-GOVERNMENTAL
                              DEVELOPMENT OF SPACE

                              By: /s/ Walt Anderson
                                 --------------------------
                              Name: Walt Anderson
                              Title: President

                              GOLD & APPEL TRANSFER, S.A.

                              By: /s/ Walt Anderson
                                 --------------------------
                              Name: Walt Anderson
                              Title: Attorney-in-Fact

                              NORTEL NETWORKS INC.

                              By: /s/ Mitchell L. Stone
                                 --------------------------
                              Name: Mitchell L. Stone
                              Title: Director

                              WILLIAMS COMMUNICATIONS, INC.

                              By: /s/ Gordon C. Martin Jr.
                                 --------------------------
                              Name: Gordon C. Martin Jr.
                              Title: SVP, Global Network Svcs.

                                       5
<PAGE>

                                  SCHEDULE 1
                                  ----------

                              SERIES B PURCHASERS
<TABLE>
<CAPTION>

<S>     <C>                           <C>
1.      Gold & Appel Transfer, S.A.   1023 31st Street, N.W.
                                      Washington, D.C.  20007
                                      Attn:  Walter Anderson, Attorney in Fact

2.      Nortel Networks Inc.          GSM 991 15 A40
                                      2221 Lakeside Boulevard
                                      Richardson, TX 75082
                                      Attn: Vice President, Customer Finance

3.      Allied Capital Corporation    1919 Pennsylvania Avenue, N.W., 3rd Floor
                                      Washington, D.C.  20037
                                      Attn:  Scott S.  Binder, Principal
                                             Thomas H. Aiken, Principal
</TABLE>
                              SERIES C PURCHASERS
<TABLE>

<S>     <C>                            <C>
1.      Gold & Appel Transfer, S.A.    1023 31st Street, N.W.
                                       Washington, D.C.  20007
                                       Attn:  Walter Anderson, Attorney in Fact

2.      Nortel Networks Inc.           GSM 991 15 A40
                                       2221 Lakeside Boulevard
                                       Richardson, TX 75082
                                       Attn: Vice President, Customer Finance
                                             North America

3.      Allied Capital Corporation     1919 Pennsylvania Avenue, N.W., 3rd Floor
                                       Washington, D.C.  20037
                                       Attn: Scott S.  Binder, Principal
                                             Thomas H. Aiken, Principal

4.      Foundation for the             c/o:  Walt Anderson
        International Non-Governmental       1023 31st Street, N.W.
        Development of Space                 Washington, D.C.  20007

5.      Williams Communications, Inc.   One Williams Center
                                        Suite 4100
                                        Tulsa, OK  74172
                                        Attn: S. Miller Williams, Vice President
                                              Lisa Manning, Esq.
</TABLE>

                                       6<PAGE>

                                                                     Exhibit 4.9

                           INVESTOR RIGHTS AGREEMENT

          THIS INVESTOR RIGHTS AGREEMENT (this "Agreement") is entered into as
of July 23, 1999 (the "Effective Date"), by and among NET-TEL COMMUNICATIONS,
INC., a Delaware corporation (the "Company") and certain persons and entities
listed on the signature page to this Agreement hereto, as such Schedule may be
amended to add persons purchasing up to an additional 647 shares of Series B (as
defined below) (each a "Purchaser" and collectively, the "Purchasers").

          WHEREAS, the Company has issued to the Purchasers 5,821.47 shares of
the Company's Series B Convertible Preferred Stock (the "Series B Preferred
Stock");

          WHEREAS, the Company and the Purchasers desire to enter into this
Agreement in order to provide for certain rights and responsibilities as set
forth herein; and

          WHEREAS, capitalized terms used in this Agreement shall have the
meaning ascribed to them in Section 4 hereof.
                            ---------

          NOW, THEREFORE, for and in consideration of the foregoing and of the
mutual covenants and agreements hereinafter set forth, the parties hereto agree
as follows:

1.  RIGHT OF First Refusal; Right of CO-SALE

    1.1   Transfers by Purchasers

          Except as permitted by Section 1.2, f any of the Purchasers desires to
          accept an offer to buy its Series B Preferred Stock (any such Person a
          "Selling Person") (except as permitted by Section 1.2), the Selling
          Person shall deliver a written notice (the "Sale Notice") to the
          (other) Purchasers, at least ten (10) business days prior to the
          proposed sale, which such notice shall specify the terms and
          conditions upon which the proposed sale is intended to be consummated.
          The (other) Purchasers shall have the option to either exercise a
          right of first refusal by purchasing such offered Series B Preferred
          Stock, or to participate in such sale as co-sellers, either way in the
          manner hereinafter set forth.  To exercise either option, any
          interested Purchaser(s) shall give written notice (the "Participation
          Notice") of their election to either exercise a right of first
          refusal, or participate in such sale as co-sellers, to the Selling
          Person within ten (10) business days after receipt of the Sale Notice.
          Thereupon, each of the Purchasers shall have the right to either
          purchase the offered Series B Preferred
<PAGE>

          Stock upon the same terms and conditions specified in the Sale Notice
          pro rata with the other interested Purchasers, or to sell their Series
          B Preferred Stock to the proposed purchaser upon the same terms and
          conditions specified in the Sale Notice, pro rata with the Selling
          Person and all other Purchasers delivering a Participation Notice
          based upon the then current holdings of equity securities of the
          Company, on a fully diluted basis, of the Selling Person and all such
          Purchasers delivering a Participation Notice; provided, however, that
                                                -----------------
          notwithstanding any other provision of this Section 1.1, no Selling
          Person shall be required to sell to any interested Purchaser(s)
          exercising a right of first refusal hereunder unless the Selling
          Person receives timely Participation Notices containing subscriptions
          for all of the shares of Series B Preferred Stock proposed to be sold
          pursuant to the Sale Notice in which case the Selling Person and any
          Purchaser exercising a co-sale right shall sell to the interested
          Purchaser in accordance with this Section 1.1.  In the event a Selling
          Person receives one or more Participation Notices requesting co-sale,
          the number of Series B Preferred Stock to be sold by the Selling
          Person (whether sold pursuant to the Sale Notice or to interested
          Purchasers pursuant to a Purchase Notice) shall be reduced, pro rata
          as described above, by the Series B Preferred Stock to be sold by such
          Purchasers.  If any of the Purchasers exercise either such option, it
          shall bear its pro rata portion of expenses incident to such sale.
          Failure by the any of the Purchasers to exercise the option within the
          ten (10) business day period shall be deemed a declination of any
          right of such Purchaser to participate in such sale, provided that
          such sale is completed within ninety (90) days of expiration of such
          ten (10) business day period at a price and on terms and conditions
          substantially similar to those set forth in the Sale Notice.  Failure
          to meet the foregoing conditions shall require a new Sale Notice and
          right of first refusal and/or right of co-sale with respect to such
          sale.  Notwithstanding any other provision of this Agreement, no sale
          may be made to any Person who is not a Purchaser, unless such Person
          executes a joinder agreement in a form satisfactory to the Company and
          becomes a "Purchaser" under this Agreement.

     1.2  Excluded Transfers

          Any Purchaser may transfer its Series B Preferred Stock without
compliance with Section 1.1, upon at least five (5) business days prior written
notice of such transfer to the Company (a) to an Affiliate of such Purchaser or
(b) in the case of a Purchaser who is a lender to  the Company or a Subsidiary
under a credit facility, to any Person who is an assignee or participant in all
or a portion of the loans under such credit facility; provided, that any such
                                                      --------
transferee shall execute a joinder agreement in a form reasonably satisfactory
to the Company pursuant to which such transferee becomes a "Purchaser" under
this Agreement.

                                      -2-
<PAGE>

     1.3  Transfers by James F. Kenefick

          If James F. Kenefick or any of his Affiliates (any such person a
"Founder") desires to accept an offer to buy any equity securities of the
Company which are owned by such Founder (except in a Kenefick Excluded Transfer
(as defined below),  such Founder shall deliver a Sale Notice to the
Purchasers, at least ten (10) business days prior to the proposed sale, which
such notice shall specify the terms and conditions upon which the proposed sale
is intended to be consummated.  The (other) Purchasers shall have the option to
either exercise a right of first refusal by purchasing such offered equity
securities, or to participate in such sale as co-sellers, either way in the
manner hereinafter set forth.  To exercise either option, any interested
Purchaser(s) shall give a "Participation Notice" of their election to either
exercise a right of first refusal, or participate in such sale as co-sellers, to
the transferring Founder within ten (10) business days after receipt of the Sale
Notice.  Thereupon, each of the Purchasers shall have the right to either
purchase the offered equity securities upon the same terms and conditions
specified in the Sale Notice, pro rata with the other interested Purchasers, or
to sell their Series B Preferred Stock to the proposed purchaser upon the same
terms and conditions specified in the Sale Notice, pro rata with the
transferring Founder and all other Purchasers delivering a Participation Notice
based upon the then current holdings of equity securities of the Company, on a
fully diluted basis, of such transferring Founder and all such Purchasers
delivering a Participation Notice; provided, however, that notwithstanding any
                                   -----------------
other provision of this Section 1.2, the transferring Founder shall not be
required to sell to any interested Purchaser(s) exercising a right of first
refusal hereunder unless the transferring Founder receives timely Participation
Notices containing subscriptions for all of the shares of Series B Preferred
Stock proposed to be sold pursuant to the Sale Notice in which case the Selling
Person and any Purchaser exercising a co-sale right shall sell to the interested
Purchaser in accordance with this Section 1.1.  In the event the transferring
Founder receives one or more Participation Notices requesting co-sale, the
number of equity securities to be sold by the transferring Founder (whether sold
pursuant to the Sale Notice or to interested Purchasers pursuant to a Purchase
Notice) shall be reduced, pro rata as described above, by the Series B Preferred
Stock to be sold by such Purchasers.  If any of the Purchasers exercise either
such option, it shall bear its pro rata portion of expenses incident to such
sale.  Failure by the any of the Purchasers to exercise the option within the
ten (10) business day period shall be deemed a declination of any right of such
Purchaser to participate in such sale, provided that such sale is completed
within ninety (90) days of expiration of such ten (10) business day period at a
price and on terms and conditions substantially similar to those set forth in
the Sale Notice.  Failure to meet the foregoing conditions shall require a new
Sale Notice and right of first refusal and/or right of co-sale with respect to
such sale.  For purposes of this Section  1.3, a "Kenefick Excluded Transfer"
means a transfer of equity securities (a) pursuant to the applicable laws of
descent and distribution, (b) to or among Mr. Kenefick's family group (which
shall include his parents, siblings, spouse, descendants, whether natural or
adopted, and any trust established or maintained for the benefit of any of the
foregoing), or (c) made as a charitable contribution; provided, however, that
any such transferee described in clause (a) or (b) shall execute a joinder
agreement in a form satisfactory to the Company agreeing to be bound by the
provisions of this Section 1.3 as a "Founder".

                                      -3-
<PAGE>

2.   ADDITIONAL COVENANTS OF THE COMPANY

     From and after the date hereof, the Company hereby covenants and agrees
with the Purchasers as follows:

     2.1. Books and Records.

          The Company shall, and shall cause its Subsidiaries to, keep and
maintain adequate and proper books and records of account, in which complete
entries are made in accordance with generally accepted accounting principles
consistently applied and in accordance with all applicable laws, rules, and
regulations, reflecting all financial and other transactions of the Company and
its Subsidiaries normally or customarily included in books and records of
account of companies engaged in the same or similar businesses and activities as
the Company and its Subsidiaries.

     2.2. Access and Examination Rights.

          Upon the reasonable request of the Purchasers, the Company shall
permit the Purchasers and any agents or representatives of the Purchasers to
visit and inspect the properties of the Company and its Subsidiaries, to examine
and make abstracts from any of the books and records of the Company and its
Subsidiaries (including agreements, licenses, and similar documents) at any
reasonable time and as often as the Purchasers or such agents or representatives
may reasonably request, and to discuss the business, operations, prospects,
Assets and condition (financial or otherwise) of the Company and its
Subsidiaries with any of the officers, directors, employees, agents, or
representatives of the Company and its Subsidiaries; provided, however, that
                                                     --------  -------
such rights of access and examination shall be subject to such security,
confidentiality and safety rules and regulations as the Company and its
Subsidiaries may have in effect from time to time that are applicable to all
visitors to its facilities and to applicable Laws, including those applying to
classified material and facilities.

     2.3. Financial and Business Information.

          The Company shall furnish to the Purchasers:

          (a) as soon as available and in any event within one hundred twenty
(120) days after the end of each fiscal year of the Company, a copy of the
audited balance sheet of the Company as of the end of such fiscal year and the
related audited statements of income, stockholders' equity, and changes in
financial condition for such fiscal year, all prepared in reasonable detail, and
certified by

                                      -4-
<PAGE>

independent certified public accountants of recognized national standing as
presenting fairly the financial position of the Company and approved by the
Board of Directors, including footnotes and setting forth in comparative form
the corresponding figures for the corresponding period of the preceding fiscal
year and the figures for such period set forth in the operating plan and budget
delivered by the Company;

          (b) as soon as available and in any event within sixty (60) days after
the end of each fiscal quarter of the Company (other than the last quarter of
each fiscal year) in the case of quarterly statements and within thirty (30)
days after the close of each month of each fiscal year in the case of monthly
statements, a copy of the unaudited balance sheet of the Company as of the end
of such quarter or month and the related unaudited statements of income,
stockholders' equity, and changes in financial condition of the Company for the
periods commencing at the end of the previous quarter or month and ending at the
end of such quarter or month and commencing at the beginning of the fiscal year
and ending at the end of such quarter or month, in each case including footnotes
and setting forth in comparative form the corresponding figures for the
corresponding period of the preceding fiscal year and, with respect to monthly
statements only, the figures for such period set forth in the operating plan and
budget delivered by the Company; and

          (c) promptly after the sending or filing thereof, copies of all
financial statements and reports that the Company sends to its stockholders or
any third party lender of the Company (including, without limitation, any
financial statements and reports sent to a lender under the Senior Secured
Credit Facility.

     2.4. Observer.

          Any Purchaser holding at least 2,000 shares of Series B Preferred
Stock, and so long as such Purchaser continues to beneficially own at least
2,000 of Series B Preferred Stock or Common Stock, may designate one person to
serve as an observer (an "Observer").  Except in cases where attendance at
meetings or receipt of information would cause the attorney-client privilege
between the Company and its counsel to be adversely affected or in cases in
which the Board of Directors is considering a contract between the Company and
one or more of the Purchasers or one of their Affiliates or in which the
Purchasers or one of their Affiliates has a financial interest, an Observer
shall be entitled (i) to receive the same notice in respect of all meetings
(both regular and special) of the Board of Directors and each committee thereof
as required to be furnished to members of the Board of Directors of such
committee by law or by the certificate of incorporation or the bylaws of the
Company, (ii) to attend all meetings of the Board of Directors and each
committee thereof, and (iii) to receive all information and reports which are
furnished to members of the Board of Directors and each committee thereof
(including the Audit Committee and Compensation Committee) at the time so
furnished.  An Observer may share any information gained from presence at such
meetings with the Purchaser

                                      -5-
<PAGE>

that designated such Observer and such Purchaser's employees, officers,
directors, attorneys and advisors (collectively, the "Purchaser's
Representatives") solely on a need-to-know basis, but such information shall
otherwise be kept confidential by the Observer, Purchaser and Purchaser's
Representatives to the same extent that financial information or other
confidential information with regard to the Company is required to be kept
confidential in accordance with Section 3.1.
                                -----------

     2.5.  Reserve for Conversion Shares.
           -----------------------------

       The Company shall at all times reserve and keep available out of its
     authorized but unissued shares of Common Stock, for the purpose of
     effecting the conversion of the Series B Preferred Stock and otherwise
     complying with the terms of this Agreement, such number of its duly
     authorized shares of Common Stock as shall be sufficient to effect the
     conversion of the Series B Preferred Stock from time to time outstanding or
     otherwise to comply with the terms of this Agreement.  If at any time the
     number of authorized but unissued shares of Common Stock shall not be
     sufficient to effect the conversion of the Series B Preferred Stock or
     otherwise to comply with the terms of this Agreement, the Company will take
     such corporate action as may be necessary to increase its authorized but
     unissued shares of Common Stock to such number of shares as shall be
     sufficient for such purposes.  The Company will obtain any authorization,
     consent, approval or other action by or make any filing with any court or
     administrative body that may be required under applicable state securities
     laws in connection with the issuance of shares of Common Stock upon
     conversion of the Series B Preferred Stock.

     2.6. Rule 144A Information.  The Company shall, at all times during
          ---------------------
          which it is neither subject to the reporting requirements of Section
          13 or 15(d) of the Securities Exchange Act of 1934, as amended (the
          "Exchange Act"), nor exempt from reporting pursuant to Rule 12g3-2(b)
          under the Exchange Act, provide in writing, upon the written request
          of the Purchasers or a prospective buyer of the Series B Preferred
          Stock or shares of Common Stock issued upon conversion of the Series B
          Preferred Stock from the Purchasers, all information required by Rule
          144A(d)(4)(i) of the General Regulations promulgated by the Securities
          Exchange Commission under the Securities Act ("Rule 144A
          Information"). The Company's obligations under this Section 2.6 shall
                                                              -----------
          at all times be contingent upon the Purchasers obtaining from the
          prospective buyer of Series B Preferred Stock or shares of Common
          Stock issued upon conversion of the Series B Preferred Stock a written
          agreement to take all reasonable precautions

                                      -6-
<PAGE>

          to safeguard the Rule 144A Information from disclosure to anyone other
          than a person who will assist such buyer in evaluating the purchase of
          any Series B Preferred Stock or of Common Stock issued upon conversion
          of the Series B Preferred Stock, and the Requesting Purchaser agrees
          that it may be held strictly liable and fully responsible for any
          damages suffered by the Company as a result of a disclosure of the
          Rule 144 Information by any such person.

          2.7   Restricted Corporate Actions.  The Company will not, without
                ----------------------------
                the vote or written approval of the holders of 66 2/3% of the
                outstanding Series B Preferred Stock, take any of the following
                actions:

          1.    engage in any business outside the Telecommunications Business .
                For purposes of this Section 2.7 and as otherwise used in this
                Agreement, "Telecommunications Business" shall mean the business
                of (i) transmitting, or providing services relating to the
                transmission of , voice, data or video through owned or leased
                transmission facilities, (ii) constructing, creating, developing
                or marketing communications-related network equipment, software
                and other devices for use in, or performing, developing or
                marketing services related to, a telecommunications business, or
                (iii) evaluating, participating or pursuing any other activity
                or opportunity that is primarily related to those referred to in
                clauses (i) or (ii) above;
          2.    make any loans to any employees, officers or directors of the
                Company in the ordinary course of business that exceed
                $1,000,000 in aggregate amount at any time outstanding, other
                than commission advances and travel or miscellaneous cash
                advances in the ordinary course of business and loans to
                employees seeking to exercise stock options issued pursuant to
                any of the Plans, the proceeds of which are used to exercise
                such options; or

          3.    enter into any business arrangement or agreement (other than a
                stock option, stock purchase or similar agreement with respect
                to Employee Stock) with any officer, director or affiliate of
                the Company on terms less favorable to the Company than an arms-
                length transaction.
          4.    Enter into any registration rights agreement granting
                registration rights to any person which are senior in any
                respect to the registration rights of the holders of the Series
                B Preferred Stock.

3.   COVENANTS OF THE PURCHASERS.

     3.1. Confidentiality.

          Purchasers will, and will cause their Affiliates, Observers and
          Purchaser's Representatives to, treat and hold as confidential all of
          the Confidential Information, refrain from using any of the
          Confidential

                                      -7-
<PAGE>

          Information except in connection with this Agreement, and following
          the disposition by Purchaser of its Series B Preferred Stock, deliver
          promptly to the Company or destroy, at the request and option of the
          Company, all tangible embodiments of the Confidential Information
          which are in its possession; provided that nothing herein shall
                                       ---------
          prevent any Purchaser from disclosing such information (a) to any
          other Purchaser, (b) upon the order of any court or administrative
          agency, (c) which has been publicly disclosed, (d) in connection with
          any litigation to which such Purchaser may be a party, (e) to the
          extent reasonably required in connection with the exercise of any
          right or remedy under the Loan Documents, (f) to such Purchaser's
          legal counsel and independent auditors, and (g) to any actual or
          proposed Transferee all or part of its Series B stock, so long as such
          actual or proposed Transferee agrees to be bound by the provisions of
          this Section 3.1.
               ------------

4.   RESTRICTIONS ON TRANSFER
     ------------------------

     4.1.  The Series B Preferred Stock may only be transferred in accordance
with applicable securities laws and Section 1 of this Agreement.  The Company
may, as a condition to any such transfer, require an opinion of counsel from
counsel to any such transferor, that such transfer has been made in accordance
with applicable securities laws.  Each of the Purchasers acknowledges and agrees
that the stock certificate(s) evidencing the Series B Preferred Stock shall
contain a legend regarding the transfer restrictions set forth in this
Agreement.

5.   DEFINITIONS

     Capitalized terms used in this Agreement shall have the meaning ascribed to
them as follows:

          "Affiliate(s)" means:  (a) with respect to a person, any member of
such person's family; (b) with respect to an entity, any officer, director,
stockholder, partner or investor of or in such entity or of or in any Affiliate
of such entity; and (c) with respect to a person or entity, any person or entity
which directly or indirectly, through one or more intermediaries, Controls, is
Controlled by, or is under common Control with such person or entity.

          "Agreement" has the meaning set forth in the Preamble to this
Agreement.

                                      -8-
<PAGE>

          "Assets" means assets of every kind and everything that is or may be
available for the payment of liabilities (whether inchoate, tangible or
intangible), including, without limitation, real and personal property.

          "Board of Directors" means the board of directors of the Company.

          "Common Stock" means the Company's common stock, par value $.0001 per
share.

          "Company" has the meaning set forth in the Preamble to this Agreement.

          "Confidential Information" means the Company's confidential and
proprietary information, in written, oral or other tangible or intangible forms,
including, but is not limited to, financial or furnished to a Purchaser whether
other information regarding the business plans and strategies, including,
without limitation,  ideas, strategies, memorandums, know-how, data, reports,
interpretations, financial statements and forecasts, together with all notes,
analyses, compilations, studies, interpretations or other documents prepared by
the Purchaser or its agents or representatives which contain, reflect or are
based upon, in whole or in part, the information furnished by the Company .

          "Control" means possession, directly or indirectly, of power to direct
or cause the direction of management or policies (whether through ownership of
voting securities, by contract or otherwise).

          "Employee Stock" has the meaning set forth in Section 7(e)(i)(2) of
the Series B Certificate.

          "Participation Notice" has the meaning set forth in Section 1.
                                                              ---------

          "Person" or "person" means any individual, partnership, joint venture,
corporation, trust, unincorporated organization, government or department or
agency of a government.

          "Purchase Agreement" means that certain Securities Purchase Agreement
dated as of the Effective Date by and between the Company, Gold & Appel
Transfer, S.A. and Nortel Networks Inc.

          "Purchasers" has the meaning set forth in the Preamble to this
Agreement.

          "Sale Notice" has the meaning set forth in Section 1.
                                                     ---------

          "Senior Secured Credit Facility" means a credit facility with a third
party lender(s) which permits the Company to borrow up to at least $50 million
dollars, and pursuant to which such lender(s) are granted a first priority

                                      -9-
<PAGE>

perfected security interest in Assets of the Company as security for the
repayment of such borrowings.

          "Series B Certificate" means the Certificate of Designations,
Preferences and Rights of Series B Convertible Preferred Stock filed with the
Secretary of State of the State of Delaware, as amended from time to time.

          "Series B Preferred Stock" means the Company's Series B Convertible
Preferred Stock, par value $0.0001 per share.

          "Selling Person" has the meaning set forth in Section 1.
                                                        ---------

          "Subsidiary" of any person means any corporation, partnership, joint
venture or other legal entity of which such person (either alone or through or
together with any other Subsidiary) (i) owns, directly or indirectly, fifty
percent (50%) or more of the stock, partnership interests or other equity
interests the holders of which are generally entitled to vote for the election
of the board of directors or other governing body of such corporation,
partnership, joint venture or other legal entity; or (ii) possesses, directly or
indirectly, control over the direction of management or policies of such
corporation, partnership, joint venture or other legal entity (whether through
ownership of voting securities, by agreement or otherwise).

6.   MISCELLANEOUS

     6.1. Assignment.

          Except as expressly contemplated elsewhere in this Agreement no party
hereto shall assign this Agreement, in whole or in part, whether by operation of
law or otherwise, unless the other party consents in writing.  Any purported
assignment of this Agreement contrary to the terms hereof shall be null and void
and of no force and effect.

     6.2. Entire Agreement; Amendment.

          This Agreement constitutes the entire agreement among the parties
hereto with respect to the matters provided for herein, and it supersede all
prior oral or written agreements, commitments or understandings with respect to
the matters provided for herein.  This Agreement may not be amended without the
written consent of the Company and the Purchasers holding sixty-six and two-
thirds percent (66 2/3%) of the Series B Preferred Stock.

                                      -10-
<PAGE>

     6.3. Waiver.

          No delay or failure on the part of any party hereto in exercising any
right, power or privilege under this Agreement or under any other instruments
given in connection with or pursuant to this Agreement shall impair any such
right, power or privilege or be construed as a waiver of any default or any
acquiescence therein.  No single or partial exercise of any such right, power or
privilege shall preclude the further exercise of such right, power or privilege,
or the exercise of any other right, power or privilege.  No waiver shall be
valid against any party hereto unless made in writing and signed by the party
against whom enforcement of such waiver is sought and then only to the extent
expressly specified therein.

     6.4. No Third Party Beneficiaries.

          It is the explicit intention of the parties hereto that no person or
entity other than the parties hereto is or shall be entitled to bring any action
to enforce any provision of this Agreement against any of the parties hereto,
and the covenants, undertakings and agreements set forth in this Agreement shall
be solely for the benefit of, and shall be enforceable only by, the parties
hereto or their respective successors, heirs, executors, administrators, legal
representatives and permitted assigns.

     6.5. Binding Effect.

          This Agreement shall be binding upon and shall inure to the benefit of
the parties hereto and their respective successors, heirs, executors,
administrators, legal representatives and permitted assigns.

     6.6. Governing Law.

          This Agreement, the rights and obligations of the parties hereto, and
any claims or disputes relating thereto, shall be governed by and construed in
accordance with the laws of the State of Delaware (excluding the choice of law
rules thereof).

     6.7. Notices.

          All notices, demands, requests, or other communications which may be
or are required to be given, served, or sent by any party to any other party
pursuant to this Agreement shall be in writing and shall be hand-delivered or
mailed by first-class, registered or certified mail, return receipt requested,
postage prepaid, or transmitted by telegram, telecopy, facsimile transmission or
telex, addressed as follows:

                                      -11-
<PAGE>

          (a) If to the Purchasers, to the address and numbers set forth next to
the name of each Purchaser on Schedule 1 of the Purchase Agreement.
                              ----------

          (b)  If to the Company:

          NET-tel Communications, Inc.
          1023 31st Street, N.W.
          Washington, D.C.  20007
          Attention:  Craig Bandes
          Senior      Vice President
          Tel:  (202) 295-6600
          Fax:  (202) 965-4154

Each party may designate by notice in writing a new address to which any notice,
demand, request or communication may thereafter be so given, served or sent.
Each notice, demand, request, or communication which shall be hand-delivered,
mailed transmitted, telecopied or telexed in the manner described above, or
which shall be delivered to a telegraph company, shall be deemed sufficiently
given, served, sent, received or delivered for all purposes at such time as it
is delivered to the addressee (with the return receipt, the delivery receipt, or
the answerback being deemed conclusive, but not exclusive, evidence of such
delivery) or at such time as delivery is refused by the addressee upon
presentation.

     6.8. Execution in Counterparts.

          To facilitate execution, this Agreement may be executed in as many
counterparts as may be required; and it shall not be necessary that the
signatures of, or on behalf of, each party, or that the signatures of all
persons required to bind any party, appear on each counterpart; but it shall be
sufficient that the signature of, or on behalf of, each party, or that the
signatures of the persons required to bind any party, appear on one or more of
the counterparts.  All counterparts shall collectively constitute a single
agreement.  It shall not be necessary in making proof of this Agreement to
produce or account for more than a number of counterparts containing the
respective signatures of, or on behalf of, all of the parties hereto.

     6.9. Termination.

          This Agreement shall terminate in its entirety and be of no further
force and effect upon the occurrence of a "Qualified Offering" (as defined in
Section 8 (a) of the Series B Certificate or a "Sale" (as defined in Section
5(b) of the Series B Certificate.

                                      -12-
<PAGE>

     6.10. Additional Purchaser(s).

           In the event of a Subsequent Issuance (as defined in the Purchase
Agreement), any purchaser of Series B Preferred Stock shall be deemed to be a
"Purchaser" under this Agreement and shall execute a joinder agreement in a form
which is satisfactory to the Company or become a signatory to this Agreement.

             [The remainder of this page intentionally left blank.]

                                      -13-
<PAGE>

          IN WITNESS WHEREOF, the undersigned have duly executed this Investor
Rights Agreement, or have caused this Investor Rights Agreement to be duly
executed on their behalf, as of the day and year first hereinabove set forth.

                                    COMPANY:

                                    NET-TEL COMMUNICATIONS, INC.

                                    By: /s/ James F. Kenefick
                                        ---------------------------
                                    Name:   James F. Kenefick
                                         --------------------------
                                    Title:  President
                                          -------------------------

                                    PURCHASERS:

                                    GOLD & APPEL TRANSFER, S.A.

                                    By: /s/ Walt Anderson
                                        ----------------------------
                                    Name:  Walt Anderson
                                         ---------------------------
                                    Title: Power of Attorney in Fact
                                           -------------------------

                                    WILLIAMS COMMUNICATIONS, INC.

                                    By: /s/ James W. Dutton
                                        ----------------------------
                                    Name:  James W. Dutton
                                          --------------------------
                                    Title: Vice President
                                           -------------------------

ALLIED CAPITAL CORPORATION          NORTEL NETWORKS INC.

By: /s/ Thomas H. Aiken             By: /s/ Jay R. Prestipino
    -----------------------             -----------------------------
Name: Tom Aiken                     Name: Jay R. Prestipino
      ---------------------              ----------------------------
Title: Associate                    Title: Director, Customer Finance
       --------------------                --------------------------
Dated: August 2, 1999

          The undersigned agrees to be bound by Section 1.3 of this Agreement.

          /s/ James F. Kenefick
          ----------------------------
          James F. Kenefick

                                      -14-

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