if you use AIM and live in USA, you can sign up for a phone number that accepts incoming calls for free. (outgoing calls will cost money). if you're not signed on when the calls come, it goes to a voicemail box. pretty cool http://aimphone.aol.com/
yeah.. apparently the aimphone thing isn't being implemented too well... other free phone services that ppl might be interested include: skype (as mentioned by knocturnal) standaphone (sp?) reasons you might want to try these: you dont want to use up cell phone minutes when you're at home you already have mic and speakers or headset extra number / voicemail to use as backup
