If you're forever a version or two of iOS behind because you need to wait for a carrier unlock to become available, then CutYourSim and other similar sites offering the same service could be for you.
The iPhone Dev Team today has released an updated version of Ultrasn0w unlock to fix signal bar issues on iOS 4.3.1 compatible iPhones, running on the old baseband.
The newly released Sn0wbreeze 2.4 supports Ultrasn0w unlock for iPhone 4 and 3GS users (old basebands only) which otherwise happens to be broken on the latest iOS 4.3.1 firmware.
