Zero1 Mobile

Zero1 Mobile, a new nationwide MVNO running on AT&T’s network, has just launched with an $69.99 per month unlimited data and and voice plan. For an additional $10 per month, Zero1 Mobile offers unlimited international calling to over 40 countries.

Zero1 is a bit different than other MVNOs in that it uses the data network for both data and voice.  Proprietary software installed on your device allows you to make voice calls via the data network and ensures that the quailty of calls stays high when data network connectivity weakens.

Zero1 Mobile only currently supports Windows Mobile devices, however, support for BlackBerry, Android, and other smartph0nes is in the works.

[Source]