<PAGE>   1
                                                                   EXHIBIT 10.18

                            CONSENT TO SUB-SUBLETTING

        THIS AGREEMENT (this "AGREEMENT") is made as of the 15th day of
December, 1999, by and between AETNA LIFE INSURANCE COMPANY, a Connecticut
corporation ("LANDLORD"), GENERAL MAGIC, INC., a Delaware corporation
("SUB-SUBLANDLORD"), and AVCOM TECHNOLOGIES, INC., a California corporation
("SUB-SUBTENANT"), with reference to the following facts:

        A. Landlord and At Home Corporation, a Delaware corporation, dba
Excite@Home ("TENANT") are parties to a Lease Agreement entered into by Landlord
and Classifieds2000, Inc., a California corporation, Tenant's
predecessor-in-interest ("TENANT'S PREDECESSOR-IN-INTEREST"), dated February 20,
1998 (the "MASTER LEASE"), relating to certain premises more particularly
described in the Master Lease ("PREMISES").

        B. Tenant's Predecessor-in-Interest and Sub-Sublandlord entered into
that certain sublease dated as of December 4, 1998 (the "SUBLEASE"). By the
terms of the Sublease, Tenant's Predecessor-in-Interest subleased to
Sub-Sublandlord and Sub-Sublandlord subleased from Tenant's
Predecessor-in-Interest a portion of the Premises, as more particularly
described in the Sublease ("SUBLEASE PREMISES").

        C. Sub-Sublandlord and Sub-Subtenant entered into that certain
sub-sublease dated as of December 3, 1999 (the "SUB-SUBLEASE"). By the terms of
the Sub-Sublease, Sub-Sublandlord will sub-sublease to Sub-Subtenant and
Sub-Subtenant will sub-sublease from Sub-Sublandlord a portion of the Premises,
as more particularly described in the Sub-Sublease ("SUB-SUBLEASE PREMISES").

        D. Sub-Sublandord has requested that Landlord consent to Sub-Sublandlord
sub-subletting the Sub-Sublease Premises to Sub-Subtenant pursuant to the
Sub-Sublease. Landlord has agreed to consent to the sub-subletting on the
following terms and conditions.

        NOW, THEREFORE, in consideration of the foregoing, and in consideration
of the mutual agreements and covenants hereinafter set forth, Landlord,
Sub-Sublandlord and Sub-Subtenant agree as follows:

        1. DEFINITIONS. Unless otherwise defined in this Agreement, all defined
terms used in this Agreement shall have the same meaning and definition given
them in the Master Lease.

        2. MASTER LEASE.

           2.1 The Sub-Sublease is and shall be at all times subject to all of
the terms and conditions of the Sublease and the Master Lease and,
notwithstanding anything to the contrary contained in the Sub-Sublease,
Sub-Subtenant agrees to perform all of the covenants of Sub-Sublandlord
contained in the Sublease and all of the covenants of the Tenant contained in
the Master Lease insofar as the same relate to the Sub-Sublease Premises.

           2.2 Sub-Subtenant acknowledges and agrees that the Sub-Sublease shall
at all times be subordinate to the Sublease and the Master Lease and the term of
the Sub-Sublease shall



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automatically terminate upon the termination of the Sublease or the Master Lease
for any reason whatsoever, including, without limitation, the termination of the
Master Lease prior to the expiration of the term thereof pursuant to a written
agreement by and between Landlord and Sub-Sublandlord. Notwithstanding any
provision to the contrary in the Sub-Sublease or in any other agreement,
Sub-Subtenant acknowledges that it shall have no right and there shall not be
vested in Sub-Subtenant any right to exercise rights of first refusal, options,
or other similar preferential rights, if any, given to Sub-Sublandlord under the
Master Lease.

        3. CONSENT OF LANDLORD. Landlord hereby consents to the sub-subletting
of the Sub-Sublease Premises to Sub-Subtenant pursuant to the terms of the
Sub-Sublease, provided, however, that Landlord specifically does not consent to
any provision of the Sub-Sublease which purports to amend provisions of the
Sublease or Master Lease, provides rights or benefits to Sub-Subtenant beyond
those specifically set forth in the Sublease and Master Lease, imposes
obligations on Landlord or seeks to obtain the consent of Landlord to any
actions on the part of Sub-Sublandlord or Sub-Subtenant (including, without
limitation, the making of any alterations or improvements to the Premises or the
further sub-subletting of the Premises or assignment of the Lease by
Sub-Subtenant) for which the approval of Landlord is otherwise required under
the Master Lease. Landlord's consent shall not release Sub-Sublandlord of any of
its obligations under the Sublease or release or alter the liability of
Sub-Sublandlord to pay rent and all other sums due under the Sublease and to
perform and comply with all other obligations of Sub-Sublandlord under the
Sublease. The Sub-Sublease shall not alter, amend or otherwise modify any
provisions of the Sublease or Master Lease. Landlord shall have no obligations
to any party in connection with the Sub-Sublease Premises other than those
obligations set forth in the Master Lease.

        4. ASSIGNMENT OF RENT.

           4.1 Subject to the terms of Section 4.2, Sub-Sublandlord hereby
absolutely and irrevocably assigns and transfers to Landlord Sub-Sublandlord's
rights under the Sub-Sublease to all rentals and other sums due Sub-Sublandlord
under the Sub-Sublease.

           4.2 Landlord agrees that until a default shall occur in the
performance of Tenant's obligations under the Master Lease, Sub-Sublandlord
shall have a license to receive, collect and enjoy the rentals and other sums
due Sub-Sublandlord under the Sub-Sublease (subject to any contrary provisions
of the Master Lease concerning the payment of any sub-sublease profits or "bonus
rents" to Landlord). However, said license shall automatically terminate without
notice to Sub-Sublandlord upon the occurrence of a default under the Master
Lease and Landlord may thereafter, at its option, receive and collect, directly
from Sub-Subtenant, all rentals and other sums due or to be due Sub-Sublandlord
under the Sub-Sublease. Landlord shall not, by reason of the assignment of all
rentals and other sums due Sub-Sublandlord under the Sub-Sublease, nor by reason
of the collection of said rentals or other sums from the Sub-Subtenant, nor by
reason of its approval of the Sub-Sublease, (a) be bound by or become a party to
the Sub-Sublease, (b) be deemed to have accepted the attornment of
Sub-Subtenant, or (c) be deemed liable to Sub-Subtenant for any failure of
Sub-Sublandlord to perform and comply with Sub-Sublandlord's obligations under
the Sub-Sublease. Sub-Sublandlord hereby irrevocably authorizes and directs
Sub-Subtenant, upon receipt of any written notice from Landlord stating that a
default exists under the Master Lease, to pay directly to Landlord the rents and
other income due and to



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become due under the Sub-Sublease. Sub-Sublandlord agrees that Sub-Subtenant
shall have the right to rely solely upon such notice from Landlord
notwithstanding any conflicting demand by Sub-Sublandlord or any other party.
Sub-Sublandlord hereby agrees to indemnify, defend and hold Sub-Subtenant
harmless from any and all claims, losses, liabilities, judgments, costs,
demands, causes of action and expenses (including, without limitation,
attorneys' fees and consultants' fees) (collectively, "CLAIMS") which
Sub-Subtenant may incur in relying on any written notice from Landlord and/or
paying rent and other sums due under the Sub-Sublease directly to Landlord in
accordance with this Section 4.2.

        5. INDEMNIFICATION; INSURANCE.

           5.1 Sub-Sublandlord shall indemnify and hold harmless Landlord and
Landlord's Agents, against and from any and all Claims arising from or related
to the following: (a) Sub-Subtenant's use of the Sub-Sublease Premises or any
activity done, permitted or suffered by Sub-Subtenant in, on or about the
Sub-Sublease Premises, the Building, or the Project; (b) any act or omission by
Sub-Subtenant or Sub-Subtenant's agents, advisors, employees, partners,
shareholders, directors, invitees or independent contractors (collectively,
"SUB-SUBTENANT'S AGENTS") in connection with or related to the Sub-Sublease, the
Sub-Sublease Premises, the Building, or the Project; (c) any Hazardous Material
used, stored, released, disposed, generated, or transported by Sub-Subtenant or
Sub-Subtenant's Agents in, on, or about the Sub-Sublease Premises, the Building
or the Project, including without limitation, any Claims arising from or related
to any Hazardous Material investigations, monitorings, cleanup or other remedial
action; and (d) any action or proceeding brought on account of any matter
referred to in items (a), (b), and/or (c). If any action or proceeding is
brought against Landlord by reason of any such Claims, upon notice from
Landlord, Sub-Sublandlord shall defend the same at Sub-Sublandlord's expense
with counsel reasonably satisfactory to Landlord. The obligations of
Sub-Sublandlord under this Section 5.1 shall survive any termination of the
Sub-Sublease or the Master Lease.

           5.2 Notwithstanding any provision to the contrary in the
Sub-Sublease, Sub-Subtenant shall, at Sub-Subtenant's expense, with respect to
the Sub-Sublease Premises, secure and keep in force during the term of the
Sub-Sublease such insurance as required of Tenant under the Master Lease.
Without limiting the generality of the immediately preceding sentence, the
policy or policies of such insurance shall name Landlord and its lenders, if
any, as additional insureds. A certificate evidencing such insurance shall be
delivered to Landlord promptly after the date hereof.

           5.3 Landlord and Sub-Subtenant hereby mutually waive any claim
against the other during the Term for any injury to a person or loss or damage
to any of their property located on or about the Premises, the Building or the
Project that is caused by perils covered by insurance carried by the respective
parties or required to be carried by the Master Lease or this Agreement, as
applicable, to the extent of the proceeds of such insurance actually received
(or which would have been received but for the failure of the party required to
carry the applicable insurance to actually maintain such insurance as required
under the Master Lease) with respect to such injury, loss or damage, whether or
not due to the negligence of the other party or its agents. Because the
foregoing waivers will preclude the assignment of any claim by way of
subrogation to an insurance company or any other person, each party now agrees
to immediately give to its insurer



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written notice of the terms of these mutual waivers and shall have their
insurance policies endorsed to prevent the invalidation of the insurance
coverage because of these waivers. Nothing in this Paragraph 5.3 shall relieve a
party of liability to the other for failure to carry insurance required by the
Master Lease or by this Agreement.

        6. MISCELLANEOUS PROVISIONS.

           6.1 Subject to Landlord's prior written approval of the plans and
specifications therefor (including, without limitation, the location, size, and
color of the equipment), during the Term, Sub-Subtenant may, at its sole cost
and expense, construct and maintain a radio frequency disk on the roof of the
Building (the "RADIO FREQUENCY DISK"); provided, however, Landlord shall have
the right to withhold its approval of the plans and specifications, in its sole
and absolute discretion, if the Radio Frequency Disk will affect the structural
integrity of the roof. Upon receipt of Landlord's prior written approval of the
plans and specifications as set forth herein, Sub-Subtenant shall erect the
Radio Frequency Disk in accordance with the approved plans and specifications,
in a good and workmanlike manner, in accordance with all applicable Laws now in
force or hereafter enacted and all other requirements of Landlord, and after
Sub-Subtenant has received all requisite approvals therefor (the "APPLICABLE
REQUIREMENTS"), and in a manner so as not to interfere with the use of the
Building or any adjacent building by any other tenant or occupant. Sub-Subtenant
shall at all times maintain the Radio Frequency Disk in a good, clean and safe
condition, in accordance with the Applicable Requirements, and in a manner so as
not to interfere with the use of the Building or any adjacent building by any
other tenant or occupant. Sub-Subtenant shall have access to the roof only when
accompanied by Landlord on Monday through Friday during normal business hours.
Upon the expiration or sooner termination of this Lease or Sub-Subtenant's right
to possession of the Premises, Sub-Subtenant shall, at Sub-Subtenant's sole cost
and expense, promptly remove the Radio Frequency Disk and repair any damage to
the Building resulting therefrom. If Sub-Subtenant fails to remove the Radio
Frequency Disk within fifteen (15) days following the expiration or sooner
termination of this Lease or Sub-Subtenant's right to possession of the
Premises, Landlord may, at Sub-Subtenant's expense, remove the Radio Frequency
Disk and perform the related restoration and repair work, and use, dispose of or
take such other actions with respect to the Radio Frequency Disk as Landlord may
deem appropriate, all without compensation or payment to Sub-Subtenant.
Sub-Subtenant shall defend, indemnify and hold harmless Landlord from all
losses, claims, liabilities, judgments, costs, demands, causes of action and
expenses (including, without limitation, attorneys' fees) arising from or
relating to the construction, installation, maintenance, use or removal of the
Radio Frequency Disk. The rights granted to Sub-Subtenant pursuant to this
paragraph may not be assigned.

           6.2 Sub-Sublandlord shall pay to Landlord, upon Landlord's demand,
Landlord's reasonable fees incurred in connection with Landlord's review and
processing of documents relating to the sub-subletting of the Sub-Sublease
Premises to Sub-Subtenant.

           6.3 Sub-Sublandlord and Sub-Subtenant agree not to amend, modify,
supplement, or otherwise change in any respect the Sub-Sublease except with the
prior written consent of Landlord, which consent shall not be unreasonably
withheld.



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           6.4 This Agreement, together with the provisions of the Master Lease
relating to sub-subletting or assigning, contains the entire agreement between
the parties hereto regarding the matters which are the subject of this
Agreement. In the event of a permitted assignment under the Master Lease by
Landlord or Sub-Sublandlord of its interest in the Sublease, then, the assignee
of either Landlord or Sub-Sublandlord, as appropriate, shall automatically be
deemed to be the assignee of Landlord or Sub-Sublandlord under this Agreement,
and such assignee shall automatically assume the obligations of Landlord or
Sub-Sublandlord under this Agreement. No other assignments of this Agreement
shall be permitted, except with the written consent of all parties hereto. The
terms, covenants and conditions of this Agreement shall apply to and bind the
heirs, successors, the executors and administrators and permitted assigns of all
the parties hereto. The parties acknowledge and agree that no rule or
construction, to the effect that any ambiguities are to be resolved against the
drafting party, shall be employed in the interpretation of this Agreement. If
any provision of this Agreement is determined to be illegal or unenforceable,
such determination shall not affect any other provisions of this Agreement, and
all such other provisions shall remain in full force and effect.

           6.5 If any party hereto fails to perform any of its obligations under
this Agreement or if any dispute arises between the parties hereto concerning
the meaning or interpretation of any provision of this Agreement, then the
defaulting party or the party not prevailing in such dispute, as the case may
be, shall pay any and all costs and expenses incurred by the other party or
parties on account of such default and/or in enforcing or establishing its
rights hereunder, including, without limitation, court costs and reasonable
attorneys' fees and disbursements. Any such attorneys' fees and other expenses
incurred by any party in enforcing a judgment in its favor under this Agreement
shall be recoverable separately from and in addition to any other amount
included in such judgment, and such attorneys' fees obligation is intended to be
severable from the other provisions of this Agreement and to survive and not be
merged into any such judgment.

           6.6 This Agreement may be executed in any number of counterparts and
by different parties hereto on separate counterparts, each of which
counterparts, when so executed and delivered, shall be deemed to be an original,
and all of which counterparts, taken together, shall constitute but one and the
same instrument.




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        IN WITNESS WHEREOF, Landlord, Tenant, Sub-Sublandlord and Sub-Subtenant
have executed this Agreement as of the day and year first hereinabove written.



                             LANDLORD:  AETNA LIFE INSURANCE COMPANY,
                                        a Connecticut corporation

                                        By:   Allegis Realty Investors LLC
                                              Its Investment Advisor and Agent


                                        By: /s/ Cynthia Stevenin
                                           -------------------------------------
                                                Cynthia Stevenin
                                                Vice President


                      SUB-SUBLANDLORD:  GENERAL MAGIC, INC.,
                                         a Delaware corporation


                                        By: /s/ Rose M. Marcario
                                           -------------------------------------
                                        Print Name: Rose Marcario
                                                   -----------------------------
                                        Title: CFO
                                              ----------------------------------


                         SUB-SUBTENANT: AVCOM TECHNOLOGIES, INC.,
                                        a California corporation


                                        By:
                                           -------------------------------------
                                        Print Name:
                                                   -----------------------------
                                        Title:
                                              ----------------------------------

ACKNOWLEDGED AND APPROVED BY:

AT HOME CORPORATION, DBA EXCITE@HOME,
a Delaware corporation

By: /s/ David Tricaso
   ------------------------------------
Print Name: David Tricaso
           ----------------------------
Title: Director of Real Estate
      ---------------------------------



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        IN WITNESS WHEREOF, Landlord, Tenant, Sub-Sublandlord and Sub-Subtenant
have executed this Agreement as of the day and year first hereinabove written.



                             LANDLORD:  AETNA LIFE INSURANCE COMPANY,
                                        a Connecticut corporation

                                        By:   Allegis Realty Investors LLC
                                              Its Investment Advisor and Agent


                                        By: /s/ Cynthia Stevenin
                                           -------------------------------------
                                                Cynthia Stevenin
                                                Vice President


                      SUB-SUBLANDLORD:  GENERAL MAGIC, INC.,
                                         a Delaware corporation


                                        By:
                                           -------------------------------------
                                        Print Name:
                                                   -----------------------------
                                        Title:
                                              ----------------------------------


                         SUB-SUBTENANT: AVCOM TECHNOLOGIES, INC.,
                                        a California corporation


                                        By: /s/ Brad Bishop
                                           -------------------------------------
                                        Print Name: Brad Bishop
                                                   -----------------------------
                                        Title: CEO
                                              ----------------------------------

ACKNOWLEDGED AND APPROVED BY:

AT HOME CORPORATION, DBA EXCITE@HOME,
a Delaware corporation

By:
   ------------------------------------
Print Name:
           ----------------------------
Title:
      ---------------------------------



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