I've never been able to get Gizmo to work, on the 770 or PC.

GoogleTalk works well for me, although there's a persistent 2 to 3 second delay. My kids think it's funny. I'm betting business users would not. ;)

my solution is tapiocca, gtalk2voip ipkall forwarded to gtalk2voip then skype forwarded to ipkall. to start a call to skype use sms4skype.net.(+41762203200) the pretty well covers it all