Using mac as a softphone (voice modem)



I have been searching the net for days, trying to find some software that will work similar to skype but through my fixed landline. Basically i use skype which turns my powerbook into a speakerphone (with other skype users) but i also wanna use it to call normal phone numbers through my internal voice modem. I dont want to get a skype account and pay for credits (use it as voip), i just want a softphone to use on my regular phone line.

I used to use SuperVoice on PC but cant find anything for mac os x. I have searched google on just about every configuration of words but its all VOIP related or business PABX management software

Anyone know of any software that will do this or is there some part of the OS that will let you dial a normal phonecall through the modem and connect you via the soundcard??

thanks guys