Just two days after the iPhone Dev Team made it possible for iPhone owners to install unsanctioned applications on their devices, a new version of their carrier unlock tool ultrasn0w is now ready for prime time. The unlock tool allows jailbroken handsets to be used on carriers not approved by Apple -- provided that they use a compatible network, of course. In the U.S. that alternative is T-Mobile, but unfortunately its network can only achieve 2G/Edge speeds on the iPhone.
The new ultrasn0w 1.0-1 software unlock supports iPhone 4 (01.59 baseband), iPhone 3G and iPhone 3GS (basebands 04.26.08, 05.11.07, 05.12.01, and 05.13.04). To run the carrier unlock, users must be on a jailbroken handset and have the Cydia Store app installed. Then, you need to add ultransn0w 1.0-1 from the repository by going to Cydia> Manage> Sources> Add and typing in "http://repo666.ultrasn0w.com" in the pop up window. Once that's added, search for ultrasn0w, install the app, and let your phone restart.
As usual, before doing this remember to backup your device just to be safe. Non-U.S. iPhone buyers can avoid going through all that trouble, however. Apple is currently selling the iPhone 4 unlocked in as much as fourteen countries. This handy info-graphic compares the various out-of-contract prices of the handset around the globe.