iPhone firmware 4.1 can be unlocked using ultrasn0w but not with the usual method.
Unlock iphone 4.1 firmware free
To unlock iPhone 4.1 firmware we need to update your iPhone baseband to 06.15.00 from iPad iOS 3.2.2 (not recommended unless you really need to unlock urgently – other alternates will be available soon)
First of all check for your iPhone’s baseband and make sure it’s 05.14.02 or 05.15.04 before upgrading it to 06.15.00 baseband.
If you want to update your iOS firmware to iPad 06.15.00 and want to unlock your iPhone 4.1 firmware follow this unlock iPhone 4.1 and 4.2.1 firmware tutorial (tested on iPhone 3G and 3GS) and your iPhone would be unlocked.