<PAGE>   1
                                                                     EXHIBIT 4.3

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO WORLDCOM, INC. (THE
"COMPANY") OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND
ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER
NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS
MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

                                 WORLDCOM, INC.
                              6.400% Note Due 2005
Principal Amount                                                   No. R-1
$                                                             CUSIP US98155KAH59

   WORLDCOM, INC., a corporation duly organized and existing under the laws of
the State of Georgia (herein called the "Company," which term includes any
successor corporation under the Indenture referred to below), for value
received, hereby promises to pay to CEDE & CO., or registered assigns, the
principal sum of _________________________DOLLARS on August 15, 2005 (the
"Stated Maturity"), and to pay interest thereon from the most recent Interest
Payment Date to which interest has been paid or duly provided for, or, if no
interest has been paid, from August 11, 1998, payable semiannually in arrears on
February 15 and August 15 in each year (each, an "Interest Payment Date"),
commencing on February 15, 1999, and at Maturity, at the rate of 6.400% per
annum, until the principal hereof is paid or duly provided for. Each payment of
interest in respect of an Interest Payment Date shall include interest accrued
through the day prior to such Interest Payment Date. The interest so payable,
and paid or duly provided for, on any Interest Payment Date shall, as provided
in the Indenture, be paid to the Person in whose name this Note (or one or more
Predecessor Securities) is registered at the close of business on the Regular
Record Date for such interest, which shall be the February 1 or August 1
(whether or not a Business Day), as the case may be, next preceding such
Interest Payment Date, at the office or agency of the Company maintained for
such purpose in The City of New York, New York. Interest shall be computed on
the basis of a 360-day year consisting of twelve 30-day months.

   Except as otherwise provided in the Indenture, any such interest not so paid
or duly provided for shall forthwith cease to be payable to the Holder on the
related Regular Record Date and may either be paid to the Person in whose name
this Note (or one or more Predecessor Securities) is registered at the close of
business on a Special Record Date for the payment of such Defaulted Interest to
be fixed by the Trustee, notice whereof shall be given to Holders of Notes (as
defined below) not less than 10 days prior to such Special Record Date, or be
paid at any time in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Notes may be listed, and

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upon such notice as may be required by such exchange, all as more fully provided
in the Indenture.

   If any Interest Payment Date, any Redemption Date, the Stated Maturity or the
Maturity shall not be a Business Day (as hereinafter defined), payment of the
amount due on this Note on such date may be made on the next succeeding Business
Day; and, if such payment is made or duly provided for on such Business Day, no
interest shall accrue on such amounts for the period from and after such
Interest Payment Date, such Redemption Date, the Stated Maturity, or the
Maturity as the case may be, to such Business Day.

   Payment of the principal of (and premium, if any) and interest on this Note
at Maturity shall be made upon presentation hereof at the office or agency of
the Company, one of which will be maintained in Pittsburgh, Pennsylvania (which
initially will be the Corporate Trust Office of The Chase Manhattan Bank in
Pittsburgh, Pennsylvania) or at such other office or agency permitted under the
Indenture, including the office or agency of the Company maintained for such
purpose in the City of New York, New York. Payment of the principal of (and
premium, if any) and interest on this Note shall be payable in immediately
available funds; provided however, that payment of interest may be made at the
option of the Company by check mailed to the address of the Person entitled
thereto as such address shall appear in the Security Register. Payment of the
principal of (and premium, if any) and interest, if any, on this Note, as
aforesaid, shall be made in such coin or currency of the United States of
America as at the time of payment shall be legal tender for the payment of
public and private debts. Interest payable on any Interest Payment Date will be
paid to DTC, Euroclear and/or CEDEL, as the case may be, with respect to the
portion of this Note held for its account by Cede & Co. or the Common
Depositary, as the case may be, for the purpose of permitting such party to
credit the interest received by it in respect of this Note to the accounts of
the beneficial owners hereof.

   This Note is one of a duly authorized issue of unsecured senior debt
securities of the Company known as the Company's 6.400% Notes Due 2005, limited
to the aggregate principal amount of $2,250,000,000 (herein called the "Notes"
or the "Securities"), issued under an Indenture dated as of March 1, 1997 (such
Indenture as originally executed and delivered and as hereafter supplemented or
amended, together with the Board Resolution setting forth certain terms of the
Notes adopted on August 6, 1998 and delivered to the Trustee by the Company
pursuant to Section 301 of such Indenture, being herein called the "Indenture")
from the Company to The Chase Manhattan Bank, as successor to Mellon Bank N.A.,
as trustee (herein called the "Trustee," which term includes any other
successor trustees under the Indenture), to which Indenture, all indentures
supplemental thereto and all Board Resolutions relating thereto reference is
hereby made for a statement of the respective rights, limitations of rights,
duties and immunities thereunder of the Company, the Trustee and the Holders of
the Notes and of the terms upon which the Notes are, and are to be,
authenticated and delivered. The acceptance of this Note shall be deemed to
constitute the consent and agreement of the Holder hereof to all of the terms
and provisions of the Indenture. All capitalized terms used in this Note which
are not defined herein shall have the meaning assigned to them in the
Indenture.

   This Note shall be redeemable, as a whole or in part, at the option of the
Company, at any time or from time to time, at a Redemption Price equal to the

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greater of (i) 100% of the principal amount hereof or (ii) the sum of the
present values of the Remaining Scheduled Payments discounted to the Redemption
Date on a semiannual basis (assuming a 360-day year consisting of twelve 30-day
months) at the Treasury Rate plus fifteen basis points, plus in the case of each
of (i) and (ii) accrued interest thereon to the Redemption Date. Notice of
redemption shall be given by mail to Holders of the Notes, not less than 30 days
nor more than 60 days prior to the Redemption Date, all as provided in the
Indenture. As provided in the Indenture, on or prior to the Redemption Date, the
Company shall deposit with the Trustee or with a Paying Agent an amount of money
sufficient to pay the Redemption Price of, and (except if the Redemption Date
shall be an Interest Payment Date) accrued interest on, the Notes to be redeemed
on such date. In the event of redemption of this Note in part only, a new Note
or Notes, of like tenor, for the unredeemed portion hereof will be issued in the
name of the Holder hereof upon the surrender hereof, all as provided in the
Indenture. On and after the Redemption Date, interest will cease to accrue on
this Note (or any portion thereof) if so called for redemption.

   If an Event of Default with respect to the Notes shall occur and be
continuing, the principal of all Notes may be declared due and payable in the
manner and with the effect provided in the Indenture.

   The Notes do not have the benefit of any sinking fund obligations.

   The Company's obligations under this Note and under the covenants provided in
the Indenture are subject to defeasance and discharge as provided in the
Indenture.

   Reference is made to the further provisions of this Note set forth on the
reverse hereof, which provisions shall for all purposes have the same effect as
if set forth at this place.

   Unless the certificate of authentication hereon has been executed by the
Trustee by manual signature, this Note shall not be entitled to any benefit
under the Indenture or be valid or obligatory for any purpose.

   IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed under its corporate seal.

                                 WORLDCOM, INC.

Attested:
                                       By:                            Secretary
------------------------                 --------------------------

     This is one of the Securities of the series designated therein referred to
in the within-mentioned Indenture.

Dated:  August 11, 1998                   THE CHASE MANHATTAN BANK,  as Trustee

                                             By:
                                                --------------------------
                                                Authorized Representative
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                                [Reverse of Note]

                                 WorldCom, Inc.

                              6.400% Note Due 2005

     "Treasury Rate" means, with respect to any Redemption Date, the rate per
annum equal to the semiannual equivalent yield to maturity (computed as of the
second Business Day immediately preceding such Redemption Date) of the
Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue
(expressed as a percentage of its principal amount) equal to the Comparable
Treasury Price for such Redemption Date.
 
     "Comparable Treasury Issue" means the United States Treasury security
selected by an Independent Investment Banker as having a maturity comparable to
the remaining term of the Notes to be redeemed that would be utilized, at the
time of selection and in accordance with customary financial practice, in
pricing new issues of corporate debt securities of comparable maturity to the
remaining term of the Notes.

     "Independent Investment Banker" means one of the Reference Treasury Dealers
appointed by the Company.

     "Comparable Treasury Price" means, with respect to any Redemption Date, (i)
the average of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) on the third
Business Day preceding such Redemption Date, as set forth in the daily
statistical release (or any successor release) published by the Federal Reserve
Bank of New York and designated "Composite 3:30 p.m. Quotations for U.S.
Government Securities" or (ii) if such release (or any successor release) is not
published or does not contain such prices on such Business Day, (A) the average
of the Reference Treasury Dealer Quotations for such Redemption Date, after
excluding the highest and lowest of such Reference Treasury Dealer Quotations,
or (B) if the Trustee obtains fewer than four such Reference Treasury Dealer
Quotations, the average of all such quotations. "Reference Treasury Dealer
Quotations" means, with respect to each Reference Treasury Dealer and any
Redemption Date, the average, as determined by the Trustee, of the bid and asked
prices for the Comparable Treasury Issue (expressed in each case as a percentage
of its principal amount) quoted in writing to the Trustee by such Reference
Treasury Dealer at 3:30 p.m., New York City time on the third Business Day
preceding such Redemption Date.

     "Reference Treasury Dealer" means each of Salomon Brothers Inc, Credit
Suisse First Boston Corporation, Lehman Brothers, Inc., J.P. Morgan Securities
Inc., and NationsBanc Montgomery Securities LLC, and their respective
successors; provided, however, that if any of the foregoing shall cease to be a
primary U.S. Government securities dealer (a "Primary Treasury Dealer"), the
Company shall substitute therefor another nationally recognized investment
banking firm that is a Primary Treasury Dealer.

     "Remaining Scheduled Payments" means, with respect to each Note to be
redeemed, the remaining scheduled payments of the principal thereof and interest
thereon that would be due after the related Redemption Date but for such
redemption; provided, however, that, if such Redemption Date is not an Interest
Payment Date with respect to such Note, the amount of the next succeeding
scheduled interest payment thereon will be reduced by the amount of interest
accrued thereon to such Redemption Date.

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     As permitted by Section 301(15) of the Indenture, the Board Resolution
setting forth the terms of the Notes provides for certain modifications to the
Events of Default and covenants of the Indenture as applicable to the Notes, as
follows:

    (A) the definition of "Restricted Subsidiary" in Section 101 of the
  Indenture, as applicable to the Notes, has been amended to read in its
  entirety as follows: " `Restricted Subsidiary' means any Subsidiary of the
  Company if (i) such Subsidiary has substantially all of its Property in the
  United States (other than its territories and possessions) and (ii) at the end
  of the most recent fiscal quarter of the Company, the aggregate amount,
  determined in accordance with GAAP consistently applied, of securities of,
  loans and advances to, and other investments in, such Subsidiary held by the
  Company and its other Subsidiaries exceeded 10% of the Company's Consolidated
  Net Tangible Assets; provided, however, that the term Restricted Subsidiary
  shall not include (a) any Subsidiary acquired by the Company subsequent to the
  date of the Indenture unless and until such time as such corporation is
  designated by the Board of Directors as a `Restricted Subsidiary' or otherwise
  similarly treated under the Company's $12 billion bank credit facility or any
  other agreement of the Company for indebtedness for borrowed money or (b) any
  Receivables Subsidiary.";

    (B) the notice period relating to Events of Default under Section 501(4) of
  the Indenture, as applicable to the Notes, has been extended from 60 days to
  90 days;

    (C) Section 501(5), which defines as an Event of Default certain defaults
  under other indebtedness of the Company has been deleted in respect of the
  Notes; and

    (D) the last sentence of Section 1004 of the Indenture, as applicable to the
  Notes, has been amended to read in its entirety as follows: "Notwithstanding
  the foregoing, the Company may, and may permit any Restricted Subsidiary to,
  issue, assume, guarantee, or permit to exist indebtedness secured by Liens on
  Property that are not Permitted Liens without equally and ratably securing the
  Securities, provided that the sum of all such indebtedness then being issued,
  assumed or guaranteed together with such indebtedness theretofore issued,
  assumed or guaranteed that remains outstanding does not exceed 10% of the
  total assets of the Company and its Subsidiaries prior to the time such
  indebtedness was issued, assumed or guaranteed, as reflected in the Company's
  then most recent balance sheet prepared in accordance with GAAP."

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     The Indenture permits, with certain exceptions as thereby provided, the
Trustee to enter into one or more supplemental indentures for the purpose of
adding any provisions to, or changing in any manner or eliminating any of the
provisions of, the Indenture or of modifying in any manner the rights of the
Holders of Securities, in any such case, with the consent of the Holders of not
less than majority in aggregate principal amount of all Outstanding Securities
affected by such supplemental indenture; provided, however, that no such
supplemental indenture shall, without the consent of the Holder of each of the
Outstanding Securities affected thereby, affect certain rights of such Holders
as more fully described in the Indenture.

     The Indenture also contains provisions permitting the Holders of specified
percentages in principal amount of the Securities then Outstanding, on behalf of
the Holders of all Securities affected thereby, to waive certain past defaults
of the Company under the Indenture and their consequences. In addition, without
the consent of any Holder of a Security, the Indenture and the Securities may be
amended and supplemented to cure any defect, ambiguity or inconsistency, make
other changes which will not adversely affect in any material respect the rights
of the Holders or provide for certain other matters specified in the Indenture.
Any such consent or waiver by the Holder of this Note shall be conclusive and
binding upon such Holder and upon all future Holders of this Note and of any
Note issued upon the registration of transfer hereof or in exchange herefor or
in lieu hereof, whether or not notation of such consent or waiver is made upon
this Note.

     As provided in and subject to the provisions of the Indenture, the Holder
of this Note shall not have the right to institute any proceeding with respect
to the Indenture or for the appointment of a receiver or trustee, or for any
other remedy thereunder, unless such Holder shall have previously given the
Trustee written notice of a continuing Event of Default with respect to the
Notes, the Holders of not less than 25 percent in principal amount of the Notes
Outstanding shall have made written request to the Trustee to institute
proceedings in respect of such Event of Default as Trustee and offered the
Trustee reasonable indemnity and the Trustee shall not have received from the
Holders of a majority in principal amount of the Notes Outstanding a direction
inconsistent with such request, and shall have failed to institute any such
proceeding, for 60 days after receipt of such notice, request and offer of
indemnity. The foregoing shall not apply to certain suits described in the
Indenture, including any suit instituted by the Holder of this Note for the
enforcement of any payment of principal hereof or any premium or interest hereon
on or after the respective due dates expressed herein (or, in the case of
redemption, on or after the Redemption Date).

     No reference herein to the Indenture and no provision of this Note or of
the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the principal of (and premium, if any) and
interest, if any, on this Note at the times, place and rate, in the coin or
currency, and in the manner, herein prescribed.

     The Notes are issuable only in registered form, without coupons, in
denominations of $1,000 and any integral multiple of $1,000, and in book-entry
form. The Notes may be represented by one or more global Notes deposited with
DTC and registered in the name of the nominee of DTC, with certain limited
exceptions. So long as DTC or any successor depository or its nominee is the
registered Holder of a global Note, DTC, such depository or such nominee, as the
case may be, will be considered to be the sole Holder of the Notes for all
purposes of the Indenture. Except as provided below, an owner of a beneficial
interest in a global Note will not be entitled to have Notes represented by such
global Note registered in such owner's name, will not receive or be entitled to
receive physical delivery of the Notes in certificated form and will not be
considered the owner or Holder thereof under the Indenture. Each person owning a
beneficial interest in a global Note must rely on DTC's procedures and, if such
person is not a participant, on the procedures of the participant through which
such person owns its interest, to exercise any rights of a Holder under the
Indenture. If the Company requests any action of Holders or if an owner of a
beneficial interest in a global Note desires to take any action that a Holder is

<PAGE>   7

entitled to take under the Indenture, DTC will authorize the participants
holding the relevant beneficial interests to give or take such action, and such
participants will otherwise act upon the instructions of beneficial owners
holding through them.

     If at any time DTC notifies the Company that it is unwilling or unable to
continue as depository for the global Note or Notes or if at any time DTC ceases
to be a clearing agency registered under the Securities Exchange Act of 1934, as
amended, if so required by applicable law or regulation, the Company shall
appoint a successor depository with respect to such global Note or Notes. If (x)
a successor depository for such global Note or Notes is not appointed by the
Company within 90 days after the Company receives such notice or becomes aware
of such unwillingness, inability or ineligibility, (y) an Event of Default has
occurred and is continuing and the beneficial owners representing a majority in
principal amount of the Notes represented by such global Note or Notes advise
DTC to cease acting as depository for such global Note or Notes or (z) the
Company, in its sole discretion, determines at any time that all Outstanding
Notes (but not less than all) issued or issuable in the form of one or more
global Notes shall no longer be represented by such global Notes, then the
Company shall execute, and the Trustee shall authenticate and deliver,
definitive Notes of like series, rank, tenor and terms in definitive form in an
aggregate principal amount equal to the principal amount of such global Note or
Notes. If any beneficial owner of an interest in a permanent global Note is
otherwise entitled to exchange such interest for Notes of such series and of
like tenor and principal amount of another authorized form and denomination, as
contemplated by the Indenture and provided that any applicable notice provided
in the permanent global Note shall have been given, then without unnecessary
delay but in any event not later than the earliest date on which such interest
may be so exchanged, the Company shall execute, and the Trustee shall
authenticate and deliver, definitive Notes in aggregate principal amount equal
to the principal amount of such beneficial owner's interest in such permanent
global Note. On or after the earliest date on which such interests may be so
exchanged, such permanent global Note shall be surrendered for exchange by DTC
or such other depository as the Company shall specify to the Trustee; provided,
however, that no such exchanges may occur during a period beginning at the
opening of business 15 days before any selection of Notes to be redeemed and
ending on the relevant Redemption Date if the Note for which exchange is
requested may be among those selected for redemption.

     None of the Company, the Trustee, any Paying Agent or the Security
Registrar will have any responsibility or liability for any aspect of the
records relating to or payments made on account of beneficial ownership
interests in this Note in global form or for maintaining, supervising or
reviewing any records relating to such beneficial ownership interests.
Notwithstanding the foregoing, nothing herein shall prevent the Company, the
Trustee, or any agent of the Company or the Trustee, from giving effect to any
written certification, proxy or other authorization furnished by any depository,
as a Holder, with respect to this Note in global form or impair, as between such
depository and owners of beneficial interests in such global Note, the operation
of customary practices governing the exercise of the rights of such depository
(or its nominee) as Holder of such global Note.

     THE  INDENTURE  AND THE  SECURITIES  SHALL BE GOVERNED BY AND  CONSTRUED IN
ACCORDANCE  WITH THE LAWS OF THE STATE OF NEW YORK,  WITHOUT REGARD TO CONFLICTS
OF LAW PRINCIPLES THEREOF.

<PAGE>   8

     As used herein, "Business Day", when used with respect to any Place of
Payment or any other particular location referred to in this Note or in the
Indenture, means any day, other than a Saturday or Sunday, that is neither a
legal holiday nor a day on which banking institutions in that Place of Payment
or particular location are authorized or required by law, regulation or
executive order to be closed.

     The Company may cause CUSIP numbers to be printed on the Notes as a
convenience to Holders of Notes. No representation is made as to the accuracy of
such numbers as printed on the Notes, and reliance may be placed only on the
other identification numbers printed thereon.

     This Note shall not be entitled to any benefit under the Indenture or be
valid or obligatory until the Trustee or authenticating agent signs the
certificate of authenticity on the Notes.

     No recourse shall be had for the payment of the principal of (or premium,
if any) or interest, if any, on this Note, or any part hereof, or for any claim
based hereon or otherwise in respect hereof, or of the indebtedness represented
hereby, or upon any obligation, covenant or agreement under the Indenture,
against, and no personal liability whatsoever shall attach to, or be incurred
by, any incorporator, shareholder, officer or director, as such, past, present
or future, of (i) the Company or (ii) any predecessor or successor corporation
(either directly or through the Company or a predecessor or successor
corporation), whether by virtue of any constitutional provision, statute or rule
of law, or by the enforcement of any assessment or penalty or otherwise; it
being expressly agreed and understood that the Indenture and all of the Notes
are solely corporate obligations and that any such personal liability is hereby
expressly waived and released as a condition of, and as part of the
consideration for, the execution of the Indenture and the issuance of the Notes.