From Electronista:

“Apple is bound to its exclusivity deal with AT&T until at least 2010, sources have allegedly told USA Today. The newspaper asserts that AT&T agreed to the large-scale subsidies on the iPhone 3G’s pricing in exchange for a one-year extension on the provider’s sole rights for the device line in the US, pushing it back from its original 2009 date. The extension is crucial for AT&T, which is the leader in an increasingly saturated market and sees the iPhone as a tool to convert customers from other networks.”