With AT&T’s exclusive hold on the iPhone due to end soon by many accounts, many are wondering if Verizon will get their own version of the iPhone early next year… and how much that will hurt AT&T. According to analysts, a Verizon iPhone wouldn’t hurt AT&T very much, and now AT&T is echoing the sentiment themselves: we’re not worried.

AT&T Chief Randall Stephenson recently spoke at the Goldman Sachs Communacopia Conference in New York City, Stephenson stated that while the iPhone was a major success for AT&T, two-thirds of iPhone purchases came from previous AT&T customers and were not likely to switch to another network just because the iPhone opened up over there as an option.

More to the point, Stephenson says that the iPhone 4 was such a huge success that they’ve locked in a huge chunk of their existing customers into new two year contracts. Added together, Stephenson thinks it’s unlikely that a Verizon iPhone would lead to a mass defection of users.

He’s probably right, at least immediately… but this isn’t about a cataclysmic migration of users that occurs the second AT&T’s iPhone exclusivity ends. This is about the long tail defection of individual users over a period of a couple of years who are so fed up with AT&T’s clumsy service and incompetence that the only thing keeping them there is the best phone on Earth. Unless AT&T takes the quality of their service more seriously without the iPhone exclusivity than they did with, there still may very well be trouble for Ma Bell down the road.