I know this is not the news we all are expecting, let alone your OS is 5.0.1 now. But this one is recommended by the MuscleNerd and spread for the first by iClarified site.
MuscleNerd said that the standard operating system procedure for unlocking using Ultrasn0w is staying at the lowest possible baseband. He further saying those who their phone running on iOS 5.0.1 to check their build number and then downgrade it to 9A406 to 9A405 -- as Apple still signs those builds. And the earlier build number has bigger chance to be unlocked than the later build.
But also please read the following quotation from iClarified site.
We can't guarantee an unlock will be found for iOS 5.0. However, in November MuscleNerd revealed that an unlock was looking 'very promising' and was able to use an exploit to dump the baseband bootrom. However, it's not clear if or when an unlock based on that exploit will materialize.
So the choice is yours to take which one you need most, whether jailbreak your iPhone or to unlock it, choose wisely then.
Keep in mind the recommendation to downgrade or not upgrade to iOS 5.0.1 only applies to iPhone 4s, NOT iPad 2.