At this point ATT's 3g network is already fast enough for normal web browsing usage, the limiting factor is the processor and ram on the phone itself at this point.
I can hardly tell a difference between wifi and 3g on my phone, because the phone still takes time to actually load and render a site.
I can't see Apple doing a half assed 4g device. So until networks support FULL 4g (as in voice and data over 4g) I can't see them offering it as a feature. Apple isn't going to do what the EVO did and stick 2 radios in their phones. WAY to big a battery hog.
What I'm more curious about is that Verizon mentions that Global LTE and GSM roaming will come later, does that mean at some point an unlocked iphone will work on verizon?