So, iOS 4.2 GM was released today for developer and would be released for public in a few days but do you want really to get it now? We have good news, you can get your hands dirty now thanks to the powers of the internet. You do not need your UDID to execute the installation. It seems like you can't upgrade to iOS 4.2 using iTunes 10 so you may need to install iTunes 10.1 beta to commerce.