Be very careful now whenever Apple release new firmware after 2.2. Apple also make it a point to change the phone baseband which make whatever released by Dev team to unlock the phone not work. yellowsn0w for fw 2.2 will not work for the new baseband. It may take weeks or months before the new unlock apps from Dev team to function. If you have a Mac you use PwnageTool 2.2.5 to create a custom ipsw file with the old baseband and the latest version of Quickpwn to jailbreak and unlock the phone. Anyway there is not much advantage to move to 2.2.1.