1985 Carphone Motorola 4800x to gsm conversion.

[eez-28]

I've an old 80's carphone 4800x with Orange led handset and a big transceiver,25 pin socket,
but can't work to make a call because is an old analog network....
I've try to connect to Motorola international 8700 gsm,with a bypass interface,i would like,
pilotate the 8700 keyb to make a call with old handset 4800x.
The experiments is failed.
All Moto bagphone or carphone and all family of Microtac analog and gsm have the same
connection pinouts.
Are 3 the important lines for working the phone:
T data
C data
R data.
I'm looking for someone who can help me to build an interface.

Thank you!