PIC to GSM

[Gusse]

Hi Dennis,

Power the MAX232N from same source as your PIC. That is the easiest way, I think.

Then do some small modifications to your 8210.

Audio-to-Data from 2.5mm bottom connector:
1) Solder wires to Fbus Rx/Tx pads
2) Connect wires to 2.5mm audio plug (select suitable pins, proposal below)
3) Solder GND wire to 2.5mm plug
3) Put some isolator between PWB and spring contacts

Nokia 8210 Pin-out

1 - MBus
2 - GND --> MIC(-) & EAR(-)
3 - FBus-Rx --> MIC(+)
4 - FBus-Tx --> EAR(+)
5 - VPP

Then use 2.5mm stereo plug to make your own data cable to connect PIC to 8210. I would recommend to use coaxial (shielded) cable for connection to avoid GSM TX coupling to data signals.
I hope this will help you to continue your project

Edit: Image removed, but here is the URL Nokia accessories - schematics

BR,
-Gusse-