IE Market Research has released a new study that shows that AT&T may be in a position to overtake rival Verizon by 2011. They point to AT&T's higher growth rate over Verizon, and say that by 2014, AT&T should still have a lead (34.8) over Verizon's share (32.5) of the cellular market. It seems that AT&T may make full use of their iPhone exclusivity deal while they still have it. Website Electronista breaks down the study into easily digestible material.
As Electronista points out, there is no certainty to how much the end of the iPhone exclusivity deal will affect the carrier. They also mention that Android phones are becoming more popular in terms of market share, and note that half of the available Android phones are on Verizon.
However, we all know that Android is an operating system, not a phone. iOS is essentially a platform and a phone (being that it only comes on one type of phone) is holding its own considering its current availability on only one carrier.