Go Google!!

Google wants to be your phone carrier. It will work on the same kind of basis as Skype but will be able to be used over a mobile phone. Similar to the old Gizmo5 calling system. Starting around $6/month!! Downfall? You must already have a carrier of some sort but I am sure that whatever your ISP is will allow it. Great.

http://www.cnn.com/2009/TECH/11/13/google.phone.service/index.html