ha! i thought it had a modem, since it's twice the size of the portable cheap motorola of the time...
They where still quite popular even in the later days, and in under developed countries... Don't quote me on the exact values but the 'car' and 'bag' phones like that had something like a 3 Watt radio while the new generation of hand held phones coming out were limited to something like 1/2 Watt because of the proximity to the head... Thus in a day and age before the cellular network was as massive and distributed as it is today, that extra radio power made a huge difference in getting a signal in many locations... And I'm not talking about rural areas, I had a 'bag' phone back then and I lived in the suburbs of Chicago, reception was still quite patchy at the time... But, I was in my early 20s looking cool with a car phone
I think my package was like 30 minutes a month and $5 each additional minute, so it's not like I made many calls... And it was cool to everyone except the stupid cops that would instantly accuse me of being a criminal, as in their opinion criminals were the only ones that needed car phones at my age back then
the phone was connected in the serial-port-like-connector next to the antennae plug.
Was the handset integrated into the car? For bag phone use and 'portable' or aftermarket quicky installs the handset plugged right into that R45 jack, for more integrated or OEM systems they might very well have use the data port for the handset hookup...
i bet i will have a hard time desoldering anything from there without cutting around the board right?
I would place it in a toaster oven (one you don't use for food) and bring it up to reflow temp slowly... Basically start at about 300 F for 5 minutes, then 400 F for a few minutes then full blast broil/on... Remove with gloves or pliers and pluck parts for a few minutes, place back in over and repeat, you will be able to pluck stuff off no problem... Doing it with a solder iron might be a challenge, even a heat gun might not work so well for some parts, they might have huge internal thermal planes, it was common for them to do this...