SCHEDULE 14A INFORMATION
 
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                        MCI Communications Corporation
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                (Name of Registrant as Specified In Its Charter)
 
                              WorldCom, Inc.
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    (Name of Person(s) Filing Proxy Statement, if other than the Registrant)
 
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                                     [LOGO]
 
                                                                October 14, 1997
 
DEAR MCI SHAREHOLDER:
 
    As you are aware, on October 1, 1997, WorldCom announced that it will be
commencing an exchange offer to acquire all of the outstanding shares of MCI
Communications Corporation for $41.50 of WorldCom common stock per MCI share
(subject to adjustment as described in the enclosed materials). WorldCom's
combination with MCI will create one of the world's premier communications
companies, offering a full range of local, long distance, Internet and
international services.
 
    We have enclosed for your information our preliminary proxy statement and
preliminary exchange offer prospectus which contain detailed information
regarding the WorldCom proposal. You may receive the materials under separate
cover if your shares are maintained by your brokerage firm, bank or trust
company.
  In accordance with U.S. securities laws, the preliminary proxy statement
  does not include a proxy card. Once our proxy statement becomes definitive,
  you will receive another copy along with our WHITE proxy card which you can
  use to vote your shares.
 
    On October 10, 1997, MCI announced that the MCI board of directors requested
its advisors to analyze further the details of the WorldCom proposal. Following
such review, MCI may be soliciting your vote in favor of the British
Telecommunications plc (BT) acquisition of MCI. In such event, we will be
mailing to MCI shareholders of record definitive proxy materials. At that point,
you will have the opportunity to vote against the BT acquisition of MCI.
WorldCom cannot complete its exchange offer if the MCI shareholders approve the
BT acquisition. However, based on the strong support we have received from the
financial community as well as the very favorable reaction from MCI's
shareholders, we believe MCI shareholders will vote down the BT acquisition. THE
CHOICE FOR THE MCI BOARD WILL BE CLEAR -- TO RESPECT YOUR VOTE AND ALLOW THE
WORLDCOM OFFER TO PROCEED.
 
                  WORLDCOM OFFERS MCI SHAREHOLDERS A SUPERIOR
                       DEAL WITH GREATER POTENTIAL VALUE
 
HIGHER PRICE AND VALUE: The WorldCom proposal produces a significantly higher
premium than the BT proposal. By supporting WorldCom's proposal, MCI
shareholders will receive a better performing stock and will own a significantly
higher proportion of WorldCom than they would of a combined BT-MCI entity.
 
    - Based on closing stock prices on September 30, 1997, WorldCom's offer
      represents over a $12 per share premium to the value in the market of BT's
      acquisition proposal -- THAT'S A $9 BILLION PREMIUM TO THE PROPOSED BT
      ACQUISITION.

    - UNLIKE BT'S ACQUISITION PROPOSAL, WORLDCOM'S OFFER IS STRUCTURED TO BE
      TOTALLY TAX-FREE TO MCI SHAREHOLDERS.
 
    - WorldCom's transaction can close on essentially the same time frame as
      BT's acquisition of MCI.
 
BEST PERFORMING STOCK: WorldCom is dedicated to the creation of shareholder
value and has the strongest track record in the industry for stock performance.
 
    - WORLDCOM HAS PROVIDED INVESTORS WITH A TOTAL COMPOUND ANNUAL RETURN OF
      55.8%, COMPARED TO 4.3% FOR MCI AND 9.4% FOR BT, SINCE THE BEGINNING OF
      1990.
 
    - Under WorldCom's offer, MCI shareholders will receive a stock with greater
      value today that is better positioned to realize higher returns in the
      future.
 
FAR MORE SYNERGIES: Our proposal offers greater identifiable synergy benefits
than the BT proposal, as described in greater detail in the enclosed materials.
 
    - By 1999, synergies in a WorldCom-MCI merger are expected to reach at least
      $2.5 billion; by 1999, synergies in a BT acquisition of MCI are estimated
      at only $400 million.
 
    - OVER FIVE YEARS, WORLDCOM-MCI'S SYNERGIES ARE EXPECTED TO TOTAL AT LEAST
      $15 BILLION, COMPARED TO $2.4 BILLION FOR BT'S PROPOSED ACQUISITION.
 
UNIQUE STRATEGIC FIT: Together, WorldCom and MCI will have the capital,
marketing abilities and state-of-the-art network to compete more effectively
against the incumbent carriers, domestically and abroad.
 
    - Unlike BT, WorldCom is already a seasoned competitor in the U.S. local
      market with an established presence in 52 local markets that will expand
      to 86 markets following completion of the Brooks Fiber acquisition.
 
    - WORLDCOM'S LOCAL NETWORK BOTH ACCELERATES MCI'S LOCAL STRATEGY AND RESULTS
      IN SIGNIFICANT SAVINGS FOR THE COMBINED COMPANY.
 
    - WorldCom and MCI share similar legacies: pioneering the introduction of
      competition to the telecommunications marketplace and histories of
      innovation, agility and growth.
 
    - MCI'S MANAGEMENT AND EMPLOYEES WILL BE AN IMPORTANT PART OF THE COMBINED
      COMPANY.
 
                            SUPPORT A SUPERIOR OFFER
 
    We urge you to read the enclosed materials carefully. If you have any
questions about the materials, please contact MacKenzie Partners, Inc. toll-free
at (800) 322-2885 or collect at (212) 929-5500.
 
                                          Sincerely,
 
                                                          [LOGO]
                                           BERNARD J. EBBERS
                                           PRESIDENT AND CHIEF EXECUTIVE OFFICER

                DON'T JUST TAKE OUR WORD FOR IT. HERE'S WHAT THE
                 EXPERT FINANCIAL ANALYSTS HAVE PUBLICLY SAID:
 
    "We expect [WorldCom's] strong long-term momentum potential to drive the
stock to a $100 per share price target within four years. Based on what we've
seen so far, a potential MCI merger might even accelerate our aggressive
long-term price target."
 
                          RICHARD KLUGMAN, GOLDMAN, SACHS & CO., OCTOBER 1, 1997
 
    "There should be tremendous savings on MCIC's local effort as various costs
associated with the launching of a local offering will be reduced. Furthermore,
unlike BTY, WCOM should not incur the huge amount of dilution for local entry as
many overlaps will be eliminated."
 
                                    DAN REINGOLD, MERRILL LYNCH, OCTOBER 1, 1997
 
    "We believe WCOM's exchange offer is favorable from a MCIC shareholder point
of view. Aside from the fact that WCOM offered a much higher premium than BTY's
current offer (41% compared to 7.8% based on September 30th close), we believe
MCIC shareholders would look favorably on a greater ownership interest in WCOM,
roughly 45% compared to 20% stake in BTY. We also believe MCIC shareholders
would prefer owning WCOM, which is a higher growth company than BTY."
 
                                  LINDA MELTZER, UBS SECURITIES, OCTOBER 2, 1997
 
    "WorldCom's mantra of increasing shareholder return lends credibility to
this accretive expansion strategy and makes the company a must-own stock to
participate in the emerging communications revolution, in our opinion."
 
                          RAGHU RAM, WHEAT FIRST BUTCHER SINGER, OCTOBER 2, 1997
 
    "An MCI acquisition would be wildly accretive to earnings in 1999 and
beyond. Our 1999 and 2000 pro forma EPS numbers are $1.90 and $2.80
respectively. Revenue growth of 16-20% seems likely over the next few years."
 
                   TIMOTHY WELLER, DONALDSON, LUFKIN & JENRETTE, OCTOBER 2, 1997
 
    "WorldCom is rated Buy and is our single best idea in the wireline
telecommunications services industry." "The completion of the MCI deal could
raise our target price on these shares considerably, to perhaps the $60 range."
"We strongly recommend purchase of these shares. We think WorldCom deserves a
premium multiple due to its projected rapid growth rate."
 
                         GUY W. WOODLIEF, PRUDENTIAL SECURITIES, OCTOBER 3, 1997
 
    "We believe WorldCom's unsolicited bid of $41.50 per share...for
MCI...reflects a superior value proposition for MCI shareholders, management and
customers. We see no comparable business case for British Telecom to justify a
higher bid because the firm has no local presence in the United States."
 
                           WILLIAM VOGEL, MONTGOMERY SECURITIES, OCTOBER 3, 1997
 
    "... more value is created through a WorldCom/MCI marriage than through a
BT/MCI marriage because of superior operating and capital efficiencies and the
ability to accelerate the revenue growth of the combined WorldCom/MCI over the
sum of the growth rates of WorldCom and MCI independently." "In our opinion, the
WorldCom exchange offer creates more long-term value for MCI than the BT merger
would."
 
                                  ERIC STRUMINGHER, PAINEWEBBER, OCTOBER 7, 1997
 
    THE ABOVE STATEMENTS ARE EXTRACTS FROM PUBLISHED REPORTS AND PERMISSION TO
USE THESE QUOTES HAS NEITHER BEEN SOLICITED NOR OBTAINED.