The next iPhone will be called the iPhone 4G, and will, not surprisingly, support 4G (i.e., LTE) - allowing for, as every tech blogger has ever described the service, blazing fast downloads. at&t should have their LTE network up and running by 2011 (with trials starting in 2010), which will work out just perfectly for Apple's release schedule.
However, I foresee the iPhone 4G rolling out to Verizon first since their LTE deployment schedule is a bit more aggressive than at&t's. I also would not be surprised if the iPhone 4G was the first phone that Verizon carries that handles LTE.
There are rumors that the iPhone will come to Verizon in November of this year, and with Verizon expecting to have 100 million people covered with LTE by the end of this year, I don't think it's totally unrealistic to expect the iPhone 4G to launch with Verizon as early as November (which may explain why at&t is so aggressively trying to lock customers in to another 2 year commitment).
Of course, I still have another year or so with my Motorola Droid, so no matter what happens, I'll be content on the sidelines.
