I've noticed a lot additions to iOS lately, that simply wouldn't have occurred if the iPhone was still tied to one carrier in the US.
I'm sure AT&T had a lot to with holding certain features, back, but once Verizon came on board, Apple effectively are saying "It our way, or you can choose to not have the iPhone on your network."
There's no way in hell, that AT&T would've allowed iMessage to happen, a year ago.