Phone ring detector circuit

Hey, had a quick question to see if something like this might be possible, and how much would be involved. I have one phone line but it has 2 numbers, each with its own ring. Is there anyway to build a circuit that lets one ring go to one answering machine, and the other to another answering machine? Any ideas?
Thanks,

Well i see some answering machines already do this Oh well, guess my great idea was not so original