You should of course check out standard MODEM commands for initializing the device (if you havn't already), setting it to certain modes etc. Once you know that, it's just a matter of writing/reading to and from it at the right times, via a handle of some sort.

I don't have any examples :(.
Though I can remember writing stupid dialer programs in C and BASIC to annoy people a long time ago.

Would be interesting to see what people have to offer.

PS: Ever heard a room full of Windows box's ringing like a phone, without a MODEM. All at the one time ? It's really amuzing :D ;) Well. For me it was :P Especially watching a few school teachers running for the IT support hotline..