Hopefully 1700mhz band is a hidden feature in iPhone 4, supposedly the hardware in the other iPhones cannot be made compatible with it.
I don't know why people on this board would be negative about the idea of ANY additional carrier getting the iPhone. Yes, I agree that no single carrier could have handled the data demands of the iPhone, thats why everyone will get the best possible experience if the iPhone is available on as many carriers as possible.
And speaking for T-Mobile, I think that major publications have rated them to have a perfectly fine network in most metropolitan areas, sometimes even the best single carrier in a particular region.
And their plans are appreciably cheaper than AT&T. Best of all, they offer plans without a contract and without a phone subsidy where they pass on the savings to you. In other words, BYO phone, and you can get unlimited data, unlimited texting, and 500 anytime minutes for $60/month. Equivalent plan from AT&T is $85/month with 2GB a data.
Even assuming T-mob cuts data allowance to 2GB, thats still a good deal compared to AT&T. I'd love to be able to shop aggressively for an iPhone, and then save ~$300+ year on the subscription rates.
More competition can't be bad for the consumer.