Last night I wrote:

In the United States, where an iPhone 4 is free,1 customers who have the option of an iPhone choose it in overwhelming numbers (over 80% on AT&T and over 60% on Verizon). It’s increasingly clear that Android market share in the US was a direct result of iPhone carrier restrictions; those are largely gone now. Further subtract the folks who prefer Android, and the addressable market in the US isn’t as big as Frommer portrays it.

This is what increasing availability of the iPhone looks like: