So I was able to update to iOS 4.2 beta 2 on my iPhone 4 without having my device's UDID registered. All I did was alt+update to the IPSW, and it worked fine. A few people have been able to preserve their baseband while updating, but mine got updated by following their instructions, but anyway, it seemed to have worked fine. People who have tried this on their iPad keep getting the error in iTunes that tells you that you aren't registered as a developer.