As patents have always been, phone to carrier exclusivity should be something that is only allowed for a certain period of time. The iPhone being exclusive to AT&T is the best example of this situation continuing at the detriment of consumers.
Limitless exclusivity encourages monopoly, which has frequently lead to unkind business practices. Whereas putting a time limit on exclusivity protections allow new players/technologies to enter the market on a fairer playing field, give them time to establish themselves with their protections in effect, then when it times out, it keeps them from unfairly dominating a market indefinitely by allowing anyone else to compete directly with them - able to offer the same item across the board.
In the iPhone example - many, many people would like to purchase this phone to run on carriers other than AT&T but are not able to. This allows AT&T to monopolize this market on top of their already established overall market dominance, and gives iPhone consumers no choices to seek better service or better prices. They are contractually locked into financially supporting a carrier who isn't providing them with reasonable service at a reasonable price.
If the mobile market exclusivity time-out was set at a year and a half or two years - AT&T would now lose their grip on the iPhone and other wireless carriers would be free to sell iPhones and services (voice, data, etc.) at prices and capabilities that could easily rival AT&T's offerings. If AT&T wanted to remain a player, they'd have to improve their offerings.
As it is, AT&T doesn't have to do anything but lure people into expensive contracts with the promise of the iPhone - because if you want an iPhone, a service contract with AT&T is mandatory.