For what it's worth, I have a BB9700 and an iPhone.
The BB is better for things like messaging and ssh. The real keyboard makes a difference for me, and that's as a long-term iPhone user. UMA with the T-mobile version is also a nice bonus for places where I have WiFi but no/marginal coverage.
The iPhone is better for web browsing and has more apps available. In particular I use voip apps a fair bit: Acrobits, Line2/Toktumi, and occasionally Skype.
Both have reasonable IM clients - actually I use BeeJive on both.