When AT&T was the exclusive provider of the iPhone, there was much speculation about what would happen when the day came that a competitor would start selling the iPhone. Verizon started selling the iPhone in February, and enough time has now passed to take a look back and see what the impact has been.
Turns out the prognosticators predicting AT&T losing tons of customers were wrong as according to Horace Dediu, AT&T saw no impact when Verizon started selling the iPhone. The charts that Horace has on his web site show AT&T iPhone sales staying flat since the Verizon started selling the iPhone. Obviously, iPhones sold via Verizon impacted sales growth, but did not result in an exodus of customers.
The data that Horace has also shows that the vast majority of iPhone sales were outside the United States. According to Horace, US activations of new iPhones has been decreasing as a percentage of all iPhone sales worldwide, and now is at 30%, which reflects the size of the global market
One thing observers may point out is that it is possible people are waiting until the iPhone 5 is released before leaving AT&T, and that is a definite possibility. I have heard many long time iPhone owners saying they are standing pat until the iPhone 5 is available. Consequently, we may not be seeing the real impact of Verizon sales.
Another factor is that AT&T coverage, which has been poor in key markets like San Francisco, is also good in other markets. A person who is getting good service from AT&T is likely happy with their service and will stick with them.