Dude,

YES you can do it.

Just follow this step.

connect internet through Wifi from you mobile.
go to www.fring.com and download & install it.
sing up for new login id in fring.
you get skype,facebook,yahoo,msn,aim & SIP in one
select SIP in tab and enter you Voip login n pass
Bingo!!!

Hope it works out if not just PM

Happy landing!