The highly-anticipated iPhone 5 went on sale on Verizon Wireless on Friday, Sept. 21, with a secret and exciting feature: it is unlocked and works on AT&T's network as well, without requiring any hacks or tricks to switch carriers.

After a number of blog reports surfaced touting the secret of the Verizon iPhone 5, the Associated Press confirmed that the new handset on Verizon indeed accepts an AT&T "SIM card," i.e. the tiny chip that identifies a phone to a wireless network. The phone comes unlocked right out of the box, and can be active on AT&T's network effective immediately.

This is the first time that Verizon Wireless iPhones have been able to access AT&T's network without requiring comprehensive hacking procedures. The handset can be purchased with a two-year contract with Verizon, which for some means the unlock feature is not all that exciting. It does, however, give users the option of switching carriers at any given time on the same handset.

It is not clear at this point whether the unexpected feature means the phone will work with other carriers as well, such as T-Mobile USA, or just AT&T. Verizon Wireless spokeswoman Brenda Raney confirmed that Verizon iPhone 5 models are selling "unlocked," but it is not certain whether the feature is intentional.

When Sprint released the iPhone 4S last year, the phones initially came unlocked out of the box and worked on AT&T. Sprint, however, later issued software updates that turned off that capability and relocked the devices.

On the other hand, carrier policy typically allows users to unlock their phone after 90 days of service. This means that even if Verizon does issue a software update later on to turn off this feature, users should still be able to call up and ask to get the phone unlocked for world travel.

The iPhone 5 is one of the most expected smartphones of 2012, and demand is already so great that it fueled concerns over Apple's capability to keep up without facing supply shortages. Having the iPhone unlocked for use on other networks is expected to drive even more demand.