Mobivox does free Skype calls on your cell phone:
Registered Mobivox users with Skype accounts can call in to local access numbers to be connected via a virtual operator to their Skype contacts for free. The service works with landlines and mobile phones, and requires no download on your phone or PC.
This souds quite cool, but honestly I don’t have much of a use for this because I don’t use Skype much any longer.
Wandering the Interwebs 