iPhone 4 on Verizon
Great news for developers; anyone who's released an app knows that the US is by far the largest App Store market so broadening it only be a good for us.
The mobile hotspot support is interesting; I don't know if it's going to be brought to AT&T — the GSM iPhone 4 is technically capable — but I'd be shocked if international carriers weren't given the option to offer a mobile broadband package to customers.