<PAGE>
EXHIBIT 4.1a

THIS WARRANT AND THE COMMON STOCK ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY
APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE OFFERED, SOLD, TRANSFERRED OR
ASSIGNED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
SECURITIES ACT OR UPON RECEIPT BY THE COMPANY OF AN OPINION OF COUNSEL
REASONABLY SATISFACTORY TO THE COMPANY THAT REGISTRATION IS NOT REQUIRED FOR
SUCH SALE, TRANSFER OR ASSIGNMENT.



                          COMMON STOCK PURCHASE WARRANT

Original Issue Dated:  September 5, 2001              Number of Shares:  522,171


                               FASTNET CORPORATION
                               -------------------


                          Void after September 5, 2006



         1. ISSUANCE. This Warrant is issued to Edison Venture Fund IV, L.P. by
FASTNET CORPORATION, a Pennsylvania corporation (hereinafter with its successors
called the "Company").

         2. PURCHASE PRICE; NUMBER OF SHARES. Subject to the terms and
conditions hereinafter set forth, the registered holder of this Warrant (the
"Holder"), commencing on September 5, 2002, is entitled upon surrender of this
Warrant with the subscription form annexed hereto duly executed, at the
principal executive office of the Company or such other office as the Company
shall notify the Holder of in writing, to purchase from the Company at a price
per share (the "Purchase Price") of $1.27, the number of fully paid and
nonassessable shares of Common Stock, no par value per share, of the Company
(the "Common Stock") specified above. Until such time as this Warrant is
exercised in full or expires, the Purchase Price and the securities issuable
upon exercise of this Warrant are subject to adjustment as hereinafter provided.

         3. PAYMENT OF PURCHASE PRICE. The Purchase Price may be paid in cash or
by check or wire transfer.

         4. NET ISSUE ELECTION. The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares equal to the value
of this Warrant or any portion hereof by the surrender of this Warrant or such
portion to the Company, with the net issue election notice annexed hereto duly
executed, at the office of the Company. Thereupon, the Company shall issue to
the Holder such number of fully paid and nonassessable shares of Common Stock as
is computed using the following formula:

<PAGE>

                                   X = Y (A-B)
                                       -------
                                         A

where

                           X = the number of shares to be issued to the Holder
                  pursuant to this Section 4.

                           Y = the number of shares covered by this Warrant in
                  respect of which the net issue election is made pursuant to
                  this Section 4.

                           A = the fair market value of one share of Common
                  Stock, as determined below, as at the time the net issue
                  election is made pursuant to this Section 4.

                           B = the Purchase Price in effect under this Warrant
                  at the time the net issue election is made pursuant to this
                  Section 4.

         For purposes of this Warrant, if, at the time of a net issue election,
the Company's Common Stock is publicly traded, "fair market value" shall be
determined as of the last business day for which the prices or quotes discussed
in this sentence are available on or prior to the date of such election and
shall mean (i) the average (on that date) of the high and low prices of the
Common Stock on the principal national securities exchange on which the Common
Stock is traded, if the Common Stock is then traded on a national securities
exchange; or (ii) the last reported sale price (on that date) of the Common
Stock on the Nasdaq National Market, if the Common Stock is not then traded on a
national securities exchange; or (iii) the closing bid price (or average of bid
prices) last quoted (on that date) by an established quotation service for
over-the-counter securities, if the Common Stock is not reported on the Nasdaq
National Market. If the Company's Common Stock is not then publicly traded, the
"fair market value" shall be determined in good faith by the Board of Directors
of the Company.

         5. PARTIAL EXERCISE. This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

         6. ISSUANCE DATE. The person or persons in whose name or names any
certificate representing shares of Common Stock is issued hereunder shall be
deemed to have become the holder of record of the shares represented thereby as
at the close of business on the date this Warrant is exercised with respect to
such shares, whether or not the transfer books of the Company shall be closed.

                                       2
<PAGE>

         7. EXPIRATION DATE; AUTOMATIC EXERCISE. This Warrant shall expire at
the close of business on September 5, 2006, and shall be void thereafter.
Notwithstanding the foregoing, this Warrant shall automatically be deemed to be
exercised in full pursuant to the provisions of Section 4 hereof, without any
further action on behalf of the Holder, immediately prior to the time this
Warrant would otherwise expire pursuant to the preceding sentence.

         8. RESERVED SHARES; VALID ISSUANCE. The Company covenants that it will
at all times from and after the date hereof reserve and keep available such
number of its authorized shares of Common Stock as will be sufficient to permit
the exercise of this Warrant in full. The Company further covenants that such
shares as may be issued pursuant to the exercise of this Warrant will, upon
issuance and receipt of the respective purchase price therefor, be duly and
validly issued, fully paid and nonassessable and free from all taxes, liens and
charges with respect to the issuance thereof.

         9. DIVIDENDS. If after the Original Issue Date the Company shall
subdivide the Common Stock, by split-up or otherwise, or combine the Common
Stock, or issue additional shares of Common Stock in payment of a stock dividend
on the Common Stock, all references herein to a fixed number of shares of Common
Stock shall forthwith be proportionately increased in the case of a subdivision
or stock dividend, or proportionately decreased in the case of a combination,
and the Purchase Price shall forthwith be proportionately decreased in the case
of a subdivision or stock dividend, or proportionately increased in the case of
a combination.

         10. MERGERS AND RECLASSIFICATIONS. If after the Original Issue Date
there shall be any reclassification, capital reorganization or change of the
Common Stock (other than as a result of a subdivision, combination or stock
dividend provided for in Section 9 hereof), or any consolidation of the Company
with, or merger of the Company into, another corporation or other business
organization (other than a consolidation or merger in which the Company is the
continuing corporation and which does not result in any reclassification or
change of the outstanding Common Stock), or any sale or conveyance to another
corporation or other business organization of all or substantially all of the
assets of the Company, then, as a condition of such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, lawful
provisions shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall thereafter have the right to purchase, at a total price not to
exceed that payable upon the exercise of this Warrant in full, the kind and
amount of shares of stock and other securities and property receivable upon such
reclassification, reorganization, change, consolidation, merger, sale or
conveyance by a holder of the number of shares of Common Stock which might have
been purchased by the Holder immediately prior to such reclassification,
reorganization, change, consolidation, merger, sale or conveyance, and in any
such case appropriate provisions shall be made with respect to the rights and
interest of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the number
of shares issuable hereunder) shall thereafter be applicable in relation to any
shares of stock or other securities and property thereafter deliverable upon
exercise hereof.

                                       3
<PAGE>

         11. FRACTIONAL SHARES. In no event shall any fractional share of Common
Stock be issued upon any exercise of this Warrant. If, upon exercise of this
Warrant as an entirety, the Holder would, except as provided in this Section 11,
be entitled to receive a fractional share of Common Stock, then the Company
shall issue the next higher number of full shares of Common Stock, issuing a
full share with respect to such fractional share.

         12. AMENDMENT. The terms of this Warrant may be amended, modified or
waived only with the written consent of the Company and the Holder.

         13. WARRANT REGISTER; TRANSFERS, ETC.

                  A. The Company will maintain a register containing the names
and addresses of the registered Holder of this Warrant. The Holder may change
its address as shown on the warrant register by written notice to the Company
requesting such change. Any notice or written communication required or
permitted to be given to the Holder may be given by certified mail or delivered
to the Holder at its address as shown on the warrant register.

                  B. Subject to compliance with applicable federal and state
securities laws, this Warrant may be transferred by the Holder with respect to
any or all of the shares purchasable hereunder. Upon surrender of this Warrant
to the Company, together with the assignment hereof properly endorsed, for
transfer of this Warrant as an entirety by the Holder, the Company shall issue a
new warrant of the same denomination to the assignee. Upon surrender of this
Warrant to the Company, together with the assignment hereof properly endorsed,
by the Holder for transfer with respect to a portion of the shares of Common
Stock purchasable hereunder, the Company shall issue a new warrant to the
assignee, in such denomination as shall be requested by the Holder hereof, and
shall issue to such Holder a new warrant covering the number of shares in
respect of which this Warrant shall not have been transferred.

                  C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender and
cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft or destruction of such Warrant (including a
reasonably detailed affidavit with respect to the circumstances of any loss,
theft or destruction) and of indemnity reasonably satisfactory to the Company.

         14. REPRESENTATIONS AND COVENANTS OF THE HOLDER.

         This Warrant has been entered into by the Company in reliance upon the
following representations and covenants of the Holder:

                  A. INVESTMENT PURPOSE. The right to acquire Common Stock or
the Common Stock issuable upon exercise of the Holder's rights contained herein
will be acquired for investment and not with a view to the sale or distribution
of any part thereof, and the Holder has no present intention of selling or
engaging in any public distribution of the same except pursuant to a
registration or exemption.

                                       4
<PAGE>

                  B. PRIVATE ISSUE. The Holder understands (i) that the Common
Stock issuable upon exercise of this Warrant is not registered under the
Securities Act or qualified under applicable state securities laws on the ground
that the issuance contemplated by this Warrant will be exempt from the
registration and qualifications requirements thereof, and (ii) that the
Company's reliance on such exemption is predicated on the representations set
forth in this Section 14.

                  C. DISPOSITION OF HOLDER'S RIGHTS. In no event will the Holder
make a disposition of any of its rights to acquire Common Stock hereunder unless
and until (i) it shall have notified the Company of the proposed disposition,
and (ii) either (A) appropriate action necessary for compliance with the
Securities Act has been taken, or (B) an exemption from the registration
requirements of the Securities Act is available as set forth in a legal opinion
received by counsel reasonably satisfactory to the Company.

                  D. ACCREDITED INVESTOR. The Holder is an "accredited investor"
within the meaning of Rule 501 of Regulation D, as presently in effect.

         15. NO IMPAIRMENT. The Company will not, by amendment of its Articles
of Incorporation or through any reclassification, capital reorganization,
consolidation, merger, sale or conveyance of assets, dissolution, liquidation,
issue or sale of securities or any other voluntary action, avoid or seek to
avoid the observance or performance of any of the terms of this Warrant, but
will at all times in good faith assist in the carrying out of all such terms and
in the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder.

         16. GOVERNING LAW. The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the
Commonwealth of Pennsylvania.

         17. SUCCESSORS AND ASSIGNS. This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

         18. BUSINESS DAYS. If the last or appointed day for the taking of any
action required or the expiration of any right granted herein shall be a
Saturday or Sunday or a legal holiday in Delaware, then such action may be taken
or right may be exercised on the next succeeding day which is not a Saturday or
Sunday or such a legal holiday.


                            [SIGNATURE PAGE FOLLOWS]

                                       5
<PAGE>



Dated:  September ___, 2001          FASTNET CORPORATION


(Corporate Seal)                     By:
                                        ----------------------------------------

Attest:                              Title:
                                           -------------------------------------

                                       6
<PAGE>

                                  Subscription


To: FASTNET CORPORATION                              Date:______________________


         The undersigned hereby subscribes for __________ shares of Common Stock
covered by this Warrant. The certificate(s) for such shares shall be issued in
the name of the undersigned or as otherwise indicated below:


                                                     ___________________________
                                                     Signature

                                                     ___________________________
                                                     Name for Registration

                                                     ___________________________
                                                     Mailing Address



                            Net Issue Election Notice


To:  FASTNET CORPORATION                             Date:______________________


         The undersigned hereby elects under Section 4 to surrender the right to
purchase _______ shares of Common Stock pursuant to this Warrant. The
certificate(s) for the shares issuable upon such net issue election shall be
issued in the name of the undersigned or as otherwise indicated below.


                                                     ___________________________
                                                     Signature

                                                     ___________________________
                                                     Name for Registration

                                                     ___________________________
                                                     Mailing Address

                                       7
<PAGE>

                                   Assignment


         For value received ____________________________ hereby sells,

assigns and transfers unto _____________________________________________________

________________________________________________________________________________
    Please print or typewrite name and address of Assignee

________________________________________________________________________________

the within Warrant, and does hereby irrevocably constitute and appoint
_______________________ its attorney to transfer the within Warrant on the books
of the within named Company with full power of substitution on the premises.

Dated:_______________________


                                     ___________________________________________


In the Presence of:


______________________________


                                       8