All of the suggestions I'm getting make sense and it's along the lines of what we were thinking. I'm not electronics expert, that's where my partner comes into play. Originally (and forgive me for being naive) but I was thinking since the buttons must allow some sort of power to pass through them, you could tap into that and send it to the Arduino board, and have each button wired to a different pin but honestly, I'm not the electronics expert. I'm liking the sound of the DTMF signalling.
My question is now, which Arduino board do you guys think would be best to support this? And do I find these DTMF boards in the same place that I'd find the Arduino boards? For instance, are they on the Arduino store or should I look at an electronics store for one?
Edit: to clarify, yes it is a land line, and hopefully a touch tone.