The Verizon version of the iPhone 5, which went on sale Friday, comes with a secret and unexpected feature: it works on AT&T's network as well.

Confirming blog reports, The Associated Press found that the Verizon iPhone 5 accepts an AT&T "SIM card" a little chip that identifies a phone to a wireless network. The phone can then be active on AT&T's network.

It's the first time Verizon iPhones have been able to access AT&T's network without complicated hacking procedures. The feature may mean little to most buyers, since they're signing up for two years of Verizon service. But it does give them the option of switching carriers.

It's unclear whether the feature is intended and whether the phones will work with other carriers, such as T-Mobile USA.

But Verizon Wireless spokeswoman Brenda Raney confirmed Saturday that the iPhone 5 models it's selling are "unlocked."

Last year, the first shipments of the Sprint iPhone 4S were unlocked and worked on AT&T, but Sprint later issued software updates that turned off that capability.

AP