Uhhh... possibly, some old modems have a telephone jack that you can run to a phone, but the problem with those is that you crap out your net connection when you pick it up.
Though I have dialed a phone with my computer... heh... I have a program called Cool Edit, it's a sound editing app, it can also generate dial tones, so long as there's a 1ms break in between each tone, a phone will pick it up. Called my bro that way.
I think, the IP-phone work via 10/100 network card and DSL or cable modem. Connect a normal voice/data/FAX-modem to serial port, run the attached program and will work. (but the headset connect to modem)