Install iOS 6 beta Without UDID Registered on All Devices
Install iOS 6 beta 2 without UDID registration.
Apple place restrictions on who can install the iOS betas, The only way you can legitimately install iOS betas is if you get your UDID (Unique Device Identifier) registered with an iOS developer.
If your iOS device is currently jailbroken, you’ll need to backup everything and do a fresh restore of iOS 5.1.1 and complete the setup and restore your backup.
Install the last iTunes 10.6.3 apple.com/itunes/download
Execute iTune in mode as an administrator (Windows)
Restore your device to unjailbroken 5.1.1 firmware.
Click 'Extras' then 'Select IPSW' and browse for the iOS 5.1.1 firmware for your device.
Download links for iOS 5.1.1:
iPad 3 Wi-Fi - Direct link: iPad3,1_5.1.1_9B206_Restore.ipsw
iPad 3 Wi-Fi CDMA [Verizon] - Direct Link: iPad3,2_5.1.1_9B206_Restore.ipsw
iPad 3 Wi-Fi CDMA [AT&T] - Direct Link: iPad3,3_5.1.1_9B206_Restore.ipsw
iPad 2 Wi-fi - Direct Link: iPad2,1_5.1.1_9B206_Restore.ipsw
iPad 2 Wi-Fi + 3G - Direct Link: iPad2,2_5.1.1_9B206_Restore.ipsw
iPad 2 Wi-Fi + 3G CDMA - Direct Link: iPad2,3_5.1.1_9B206_Restore.ipsw
iPad 2 Wi-Fi (Rev A) - Direct Link: iPad2,4_5.1.1_9B206_Restore.ipsw
iPhone 3GS - Direct Link: iPhone2,1_5.1.1_9B206_Restore.ipsw
iPhone 4 GSM - Direct Link: iPhone3,1_5.1.1_9B208_Restore.ipsw
iPhone 4 CDMA - Direct Link: iPhone3,3_5.1.1_9B206_Restore.ipsw
iPhone 4S - Direct Link: iPhone4,1_5.1.1_9B206_Restore.ipsw
Download iOS 6 beta 2 firmware here: iOS 6 Beta 2 Firmware Direct Download Links
Open up iTunes and connect your device using your USB cable
Once you see your iOS device on the left panel, click it.
Hold down on the Alt+Option (Alt+Ctrl or Shift for Windows users) buttons and click the Check for Update button on the main panel.
Select the .ipsw for iOS 6 beta you just downloaded, and open it.
Click OK and let the iTunes do all the work.
iTunes 10.6.3 apple.com/itunes/download
iOS 6 beta 2 firmware iOS 6 beta 2 Firmware Direct Download Links
iOS 6 beta 2 Firmware Direct Download Links
/!\ EDIT /!\
iOS 6 beta 1 method used still works with beta 2 ;)