The Dev Team offer some helpfully tips for Ultrasn0w users

It looks like version 0.9 of ultrasn0w fixed up the vast majority of any problems people were seeing with the 3G/3GS carrier unlock. But hereís a brief list of fixes for anyone still seeing problems:

Unusual battery depletion is almost always caused by people choosing to ďRestore from backupĒ instead of ďSetup as new iPhoneĒ when iTunes asks you. This isnít caused by either the jailbreak or the unlock, but itís a common 3.0 snafu. The fix is to just re-run the official 3.0 restore and choose ďSetup as newĒ this time. Your music and apps and all that will still be synced, but youíll get rid of any conflicting wifi, bluetooth, or carrier settings. Then just re-run redsn0w and install ultrasn0w.
Remember, ultrasn0w works with hacktivated phones too, but donít outsmart redsn0w into thinking you donít need hacktivation! If you donít plan on using an official sim, donít activate via iTunes with such a sim. Just keep your unofficial sim at all times and let redsn0w and ultrasn0w handle hacktivation
T-Mobile in the USA doesnít use the 3G frequencies that the iPhones support, so turn off 3G in Settings->General->Network. (Some T-Mobile territories gracefully hand down to Edge mode, but most do not).
Certain unofficial plans have limitations on whether you can make calls and use data at the same time. Thatís not unlock-related.
Some people have installed previous versions of ultrasn0w using non-standard techniques. While the ultrasn0w 0.9 update should have removed all previous versions of ultrasn0w, these users may have outsmarted our removal. So make sure you donít still see /usr/bin/ultrasn0w present if youíre at ultrasn0w 0.9 (which doesnít have such a binary anymore).
If you donít need or plan to update to ultrasn0w 0.9 from a previous version, you can avoid having that red badge over Cydia by removing repo666 as a Cydia source. Donít worry, you can always add it back later If you follow us on twitter youíll be advised of any new updates anyway.