iPhone is OK if you want what it does, and as long as you don't use any of the up-market e-mail facilities (which don't work on iPhone). There's too much it won't do.
I've got TomTom 6 working on my XDA, and it's brilliant. I have a tiny phone, in my top pocket, that can navigate me across Europe, bleeps when there's a speed camera on the road (not that I'd be speeding, of course
), does e-mail and browsing, is the internet access for my laptop, etc etc etc.