EXHIBIT
10.18
   AMENDMENT
TO REVOLVING CREDIT PROMISSORY NOTE (LIBOR/PRIME)
 (Avistar
Communications Corporation)
 
 Amendment dated as of December 17, 2007
(this “Amendment”) to that
certain Revolving Credit Promissory Note dated as of December 23, 2006, by
Avistar Communications Corporation, a Delaware corporation (the “Borrower”), to the
order of JPMorgan Chase Bank, N.A. (the “Bank”), in the
maximum principal amount of $10,000,000 (the “Note”).
 
 For value received, the parties hereto
hereby agree as follows:
 
 1.
              Section
      1 of the Note is hereby amended by adding the following definitions
      thereto:
 
 “”Collateral
Agreement” means the Collateral Agreement dated the date hereof by the Guarantor
in favor of the Bank securing, among other things, the Guarantor’s obligations
to the Bank under the Guaranty, as amended from time to time.
 
 “Guarantor”
means (i) Gerald J. Burnett and (ii) Gerald J. Burnett and Marjorie J.
Burnett as Trustees for The Gerald J. Burnett and Marjorie J. Burnett Revocable
Trust.
 
 ”Guaranty”
means the Guaranty dated the date hereof by the Guarantor in favor of the Bank
guarantying, among other things, the Borrower’s obligations to the Bank under
this Note, as amended from time to time.
 
 “Security
Agreement” shall mean the Security Agreement dated the date hereof by the
Borrower in favor of the Bank securing, among other things, the Borrower’s
obligations to the Bank under this Note, as amended from time to
time.”
 
 2.
              The
      definition of “Facility Documents” in Section 1 of the Note is hereby
      amended by adding the following to the end
      thereof:  “(including, without limitation, the Collateral
      Agreement, the Guaranty and the Security
  Agreement)”.
 
 3.
              The
      address for notices to the Borrower set forth on the notary page of the
      Note is hereby deleted and the following is hereby inserted in lieu
      thereof:
 
 Attn:  Robert
Habig
 Avistar Communications
Corporation
 875 S. Grant Street, 10th
Floor
 San Mateo, CA 94402
 Telecopier:  (650)
525-1360
 Telephone:  (650)
525-3310
 
 4.
              The
      Note, as amended by this Amendment, remains in full force and
      effect.
 
 5.
              This
      Amendment shall be governed by and construed in accordance with the laws
      of the State of New York, without regard to conflicts of laws
      principles.
 
 6.
              This
      Amendment may be executed in any number of counterparts and by different
      parties hereto in separate counterparts, each of which shall be deemed to
      be an original, but all of which taken together shall constitute one in
      the same instrument.
 
 IN
WITNESS WHEREOF, the parties have caused this Amendment to be duly executed and
delivered as of the date first above written.
 
 JPMorgan
Chase Bank, N.A.
 By:           J.P.
Morgan Trust Company, N.A.
 
 
 
 By:      /s/
Nancy A.
Sheppard
 Nancy
A. Sheppard
 Managing
Director
 
 
 Avistar
Communications Corporation
 
 
 
 By:           /s/ Robert J.
Habig
 
 
 By:          /s/ Simon
B. Moss
 State
      of _________
              )
 ) ss.:
 County
      of ________
              )
 
 On the ____ day of December in the year
2007, before me, the undersigned, personally appeared ______________________,
personally known to me or proved to me on the basis of satisfactory evidence to
be the individual whose name is subscribed to the within instrument and
acknowledged to me that he/she executed the same in his/her capacity, and that
by his/her signature on the instrument, the individual, or the person upon
behalf of which the individual acted, executed the instrument.
 
 
 ____________________________________
 Notary Public
 
 
 State
      of _________
              )
 ) ss.:
 County
      of ________
              )
 
 On the ____ day of December in the year
2007, before me, the undersigned, personally appeared ______________________,
personally known to me or proved to me on the basis of satisfactory evidence to
be the individual whose name is subscribed to the within instrument and
acknowledged to me that he/she executed the same in his/her capacity, and that
by his/her signature on the instrument, the individual, or the person upon
behalf of which the individual acted, executed the instrument.
 
 
 ____________________________________
 Notary Public