iPhone 3G 4.2.1 Unlock Is there any way I can unlock an iPhone 3G with Firmware 4.2.1 and baseband 05.15.04?

I correctly installed Cydia and Ultrasn0w (under iOS 4.1.2 or something like that if I remember right) via JailbreakMe 2.0.

The Unlock seemed to work, but I accidentally updated to 4.2.1.

Is there any way I can fix this?
How about the legitimate way through AT&amp;T:

https://www.att.com/deviceunlock/client/en_US/