I wrote a simple DTMF decoder in 18 lines of perl, because I couldn't find one for linux and I like having handy things on my laptop. It only handles single tones though, not sequences, so if you want to do anything useful with it, you'll have to segment the input first.
Perhaps more amusing than the fact that I'd stay up late writing this sort of thing is that I don't have a phone to test it with. Instead, I tested it on the opening to Billy Joel's It's Just a Fantasy, and verified that other people got the same thing (516-673-1112). I didn't even bother to check first to make sure the information was out there somewhere, but of course it was.