It’s not quite wi-fi/3G Skype but it’s a start.
Skype PTT is a push to talk client for Skype to be used in conjunction with a Bluetooth enabled PC (the PC links to Skype, the phone is effectively used as a PTT headset).
The obvious limitations is that you need to remain within Bluetooth distance of your PC, and it also utilises push-2-talk which I find leads to a walkie talkie effect.
Skypejournal also cover this app
