I'm trying to create a project for my kitchen that involves using the shell of an old payphone and a modern cell phone ( perhaps iPhone ) to actually make calls. Basically, I would like the user to be able to pick up the receiver, press one of the number buttons, and have the unit auto-dail one of nine pre-defined numbers. With the microphone and speaker in the payphone being functional.
As I try to conceptualize a way to build this, here is what I came up with. Use an external iPhone microphone and speaker and place them in the handset. Use an actual iPhone as the unit that makes the call since I don't have anologue service at my house.
The part I'm a little unclear on is, how do I use the payphone button pad to somehow trigger the iPhone to make a call to 1 of 9 numbers in memory, and how do I terminate the call once the user hangs the phone up.