I can already place Skype calls over 3G ...
OK, I'm in the UK so don't have to put up with AT&T, et al, that the US do.
Using my MiFi (Wi-Fi to 3G router) from 3 I connect Skype over the Wifi connection, passing the VoIP packets along through my 3G connection. I have, hey presto, Skype over 3G.
I get 5Gb transfer for £15 a month on a rolling monthly contract, so no nasty lock-ins or expensive contracts.
Or am I missing the point?