Never one to shy away from bleeding edge technology, my co-worker Dan Diephouse (of open source web services frameworks Xfire and CXF fame) is running Fring on his iPhone and we both agree that it's pretty fringing cool.
I was able to dial Dan on Skype and he was able to call me via Skype all on our corporate wifi. He was also able to use his VZW laptop card to connect to the iPhone. Very cool and extremely useful when traveling abroad or generally on the road.
I have to admit I am bit jealous and I really wish Blackberry would realize that their devices whileare just not very fun.