Try Google. That's original! Why didn't I think of that?
Skype won't call people who aren't registered, mobiles etc so it ain't much good for general calls.
Just an emulator program to make the pc work like a phone via the modem. Can't be such a surprising requirement, surely?
MS Outlook offers to dial numbers listed in the contacts - but it doesn't work unless there is a phone cable plugged into the pc.