Best Mobile Voip

I'm curious to know which MOBILE Voip programs have worked best. One word (or name) will suffice. However, a brief explanation as to why you like it would be best. I think we can all benefit from sharing this kind of information.

Thanx for your input!

None of them really work all that well at the moment if you mean mobile in the true sense of the word.

If you need more Nomadic usage, eg you want to use your WiFi enabled handset when at home or the office then I find Fring to be about the best and it enables you to choose your own SIP based provider, so you can switch around without having to reinstall everything.

Newcomer Vopium is looking interesting also, and I'm keeping a close eye on Zer01 who intend to take VoIP truly mobile through the GSM data channel.

What do you need it for?