This seems like a bit too much trouble for some free skyping, but what do I know. IPdrum has created a product that transmits Skype audio back and forth to a cellphone which then calls you on your cellphone. I know—wha? You basically need two cellphones on the same network, preferably with free in-network calling. You leave on at home. A Skyper calls you, the cellphone dials the number to your other phone and you hear and can respond to the Skype call.
Yeah. Huh. Costs $129 and runs on XP. It only supports old Sony Ericsson and Nokia phones.
Product Page [IPdrum]
Get Skype calls on your mobile phone, free! [itWire]