After four years of wait, Apple now sells officially unlocked iPhone 4 in the U.S. This phones are officially unlocked by Apple and you will no longer need 3rd party tools such as Ultra-Snow to you use your iPhone on another GSM carrier, and you can update to all latest iOS updates without losing the unlock.
If you don’t want a multiyear service contract or if you prefer to use a local carrier when traveling abroad, the unlocked iPhone 4 is the best choice. It arrives without a micro-SIM card, so you’ll need an active micro-SIM card from any supported GSM carrier worldwide.
Apple sells the 16GB model for $649 and the 32GB model for $749.
Even though this phone is factory unlocked from Apple, it won’t work using T-Mobile’s 3G network, you will be limited to EDGE speed. I wouldn’t buy this phone to just use it on T-Mobile USA. Apple should offer this service to them as well if you own an iPhone 4. This can also mean that they are testing this model to release the real iPhone S/5 later this year supporting all network.