Depends on the cost.
I have long had an iPod Touch. It really works great. But I'm on Verizon, (and need it). I got the Eris for free, (got the offer just as my old phone broke).
I like the Eris a lot, but from using the Touch, and playing with other people's iPhones, well they just work better. (I wish either phones were the Touch's size).
With the Eris I don't miss the iPhone that much, and I would likely not spend a lot of money for the iPhone, and nothing against anyone here

, but I can see switching.
If my wife were to want a smart phone, I definitely steer her to the iPhone. The Eris, and Android, is a lot more fildlier. I don't mind so much, (few of my computers ever have the case screws in them, and I'm always beta testing), but things like battery life, and the wild west of the Andriod store and many android apps would not work for her.
--RS