Recommend an app for VOIP on Wm6.1?

[Sage]

Hi guys,

Finally in Australia 3G is getting kinda cheap.. so i am looking for an app that will let me use my SIP/VOIP provider to make phone calls on my smartphone. (Typhoon WM6.1)

Do they exist? If so what are you recommendations? :)

Thanks very much!

[netherald]

you can use skype if no such SW available now.