I'm trying to make phone calls through computer i.e. either by using a handset or sound card/mic..

can somebody pls tell me :-

1 which software(s) to use
2 where to mainly put the wires, in modem or sound card (mic, headphone etc.)
3. if i want to use handset then how to connect it...i mean when i'm connecting the handset with modem thru phone cable, i'm not getting any dial tone..

Pls help...