I have been a developer for last two years, with my phones registered with their udid. but i forgot that i had not yet registered my ip4 on the developer site before i installed the 4.1 beta.
i got all the way through to the phone restart, but when the phone rebooted, i got a message in itunes that it couldnt complete activation because it was not a properly registered developer phone. i also couldnt use itunes to find the udid of the phone, because it wouldnt get past the warning screen.
at that point, i called apple's developer support line, where a apple support tech told me that i was completely screwed -- that if i didnt register my phone first, i would have to wait until the next beta of the OS or until the final OS release. He even put me on hold to check and then came back and insisted i was out of luck.
thank god i didnt believe him. after some research, i downloaded the apple iphone configuration utility. i plugged the phone in and it immediately gave me a screen that showed the udid.
i took the udid and registered on the iphone developer site, hoping against hope that the tech was wrong. sure enough, after i registered the phone and launched itunes, the install proceeded to the final step, asked whether i wanted to set up as a new phone or from a backup, and then activated the phone. all is well.
i called the tech back and explained, and he expressed amazement that it worked. i dont know if i got lucky, or if this is normal, but i thought i'd offer my story for anyone that finds themselves in the same situation.