This is why many ATT subs have already switched over from ATT to Sprint.

FORBES: AT&T CMO: This Is How We Sold Millions More iPhones Than Verizon In 2011

McCaw was then purchased by ATT and today is ATT Wireless.

FORBES: The Secret Formula for Corporate Strategy Execution: Part 2

When one considers the unlimited plans that are Grandfathered into many ATT iPhone subs. the price differential between an ATT iPhone and a Sprint iPhone is not enough to justify many changing their plans nor is it beneficial for most subs. to go to VZ when they would end up paying substantially more.

FORBES: AT&T CMO: This Is How We Sold Millions More iPhones Than Verizon In 2011