Only payphones that have keypads that match up with its 7-pin keypad connector can easily be converted to coinless operation with that PCB. I have an Intellicall payphone that I'd like to convert to coinless, but unfortunately its keypad has a 20-pin connector, and I have no idea how to figure out the pinout in order to possibly make an adapter.
Actually, I'd rather use the internals of a tried-and-true Western Electric 2500 (and get a nice dual brass bell ringer in the process), but again, the keypad is a problem. If my payphone had a rotary dial it would be so much easier (just use the internals of a Western Electric 500 or 554; the dial would wire right up as-is).
I've had this in the back of my mind for a dozen years now, but not knowing the pinout of the Intellicall's keypad was a roadblock, and information about Intellicall stuff in general is hard to come by.
Recently I took a keypad for a 2500-type desk phone apart and when I saw its internals, it made sense as to how they work; at least for the newer type which uses a rubber membrane with carbon-coated pads for the switches, like a typical gamepad, remote control, or computer keyboard does. The older/original type that was invented by Western Electric in the 1960s uses a series of leaf switches.
I could see the layout of its matrix by looking at the PCB that sits directly beneath the rubber membrane (it only has traces on it, no components). It uses 7 pins for 12 keys, like this:
For example, when you press the "1" key, pins 1 and 5 are shorted together, and when you press the "9" key, pins 3 and 7 are shorted together, and so on.
My Intellicall keypad assembly only has the metal keys, the rubber membrane, and the traces-only PCB (so the tone-generating hardware must be located on the Intellicall chassis), but it has a 20-pin header (because it also has pins for the hookswitch, built-in electronic "ringer," handset cord, and a switch that's the same idea as an interlock switch on an arcade machine). Using a meter in continuity mode while pressing each key, it didn't take long to identify the 7 relevant pins...
... which correspond with these 7 pins on a 2500 keypad (35A11 type) that I bought for $10 so I could use its tone-generating PCB (I have no use for its plastic keys nor anything else on it):
The "DuPont connectors" that are typically used as front panel connectors in PCs fits the header pins on the Intellicall keypad's 20-pin connector, so I got some out of my junk pile and a few minutes later I had it wired to the 35A11 type tone generating PCB which in turn I wired to the ITT 427 type network of an unknown-brand 2500 type desk phone, and the Intellicall keypad worked perfectly:
I have it all mounted in the payphone housing now (with a real Western Electric 425 type network instead of the annoying ITT 427 type) and it's a fully working phone, but I'm waiting on some stuff in the mail to make a better mounting setup, one which includes a Western Electric C4A ringer (the type of ringer used in model 500 and 2500 phones, and I'll be using an older metal-framed one, not that cheapened plastic-framed version from my unknown-brand 2500), because that built-in electronic ringer is a joke.