VOIP on Smartphone

[MHC]

My Nokia N8 running Symbian has various VOIP applications available.

Has anyone tried to use their Smartphone with BT VOIP - either on a wirelss 802.11 network or the 3G data network?

If so, which application did you use and what settings are needed?

Thanks

[martin86]

I am trying to choose between a number of VOIP providers and a paid Skype package. What are the main fundamental differences between them?