I want to modify my in-car (1997 Lincoln VIII) cell phone(Motorla)
connection  to accept the newer digital cell phones. The intreface
cable that plugs into the current phone looks like it could work with
another handset. A large part of the in-car connection is just wireing
that connects to hands-free features in the phone. It seem to me that
there might be a conversion kit available some where. Please advise.

If your mark Viii has similar wiring as my 96 Town Car Cartier, I can
send you scans from the wiring schematic books.