Apple is officially selling unlocked iPhone 4 in the United States, which means consumers can now purchase the device and use it with any cellular network they wish. Aside from AT&T, the only national US carrier that's compatible with the phone is T-Mobile USA, but it can provide only phone calls and low data speeds.

Through the online Apple Store, buyers can select from a 16GB unit for $649 or a 32GB unit for $749. Both white and black versions are available. Black handset buyers have to endure a 3 day wait, white handsets have a 5+ day wait at the moment.

With the unlocked device, the buyer supplies his own SIM card that ties the phone to a network, and because many overseas carriers are compatible with the phone, international travelers can switch out their U.S. SIM card with one from the local country to avoid AT&T's international roaming fees.

iPhone watchers, however, believe there is more to the launch of the unlocked iPhone 4 than what is obvious. Selling the iPhone 4 without two-year contract could in fact mean Apple is clearing their iPhone 4 inventories to pave the way for the much anticipated iPhone 5.

Could the ‘global’ iPhone 5 come out sooner than expected?

Read: iPhone 5 could still debut in June/July