I believe it just depends on whether there's HSDPA in your area. Check it the coverage here, though it's very unspecific. There's a link at the bottom right that merely gives you a list of cities with HSDPA coverage. I think Dan is saying that until 3G is widespread, only people in certain areas who have 2nd gen iPhones will be able to use the feature. I don't necessarily think that rules it out (as far as I've seen, ATT has little say over what Apple does - they're just grateful for the exclusivity), but I do think it's a dumb feature.

I do agree, Dan, that the only guaranteed feature of the 2nd gen is 3G.

*edit*
And Tony, I'm not sure why the timing matters. Someone will correct me if I'm wrong, but I believe the price of the iPhone is independent of whether you're a new customer. I just signed up with ATT in October, and they've told me several times since that they'll sell me an iPhone for the listed price. So you could just sign up now and get one of the crappy free phones with your contract, then upgrade to the iPhone later.