For those wishing to try the beta of iPhone iOS 6 released after the WWDC 2012, here is the procedure for installation of 4 iPod, iPhone 3G, 4 and 4S and iPad 2 and 3 without owning or developer account you have registered the UDID of device.
First update iTunes to version 10.6.3.
Then download the beta of iPhone OS 6 for the device on which to perform the update (the links are easily found in google).
The device must be reset WITHOUT jailbreak (iPhone iOS 5.1.1).
Once restored (and made a backup for any restore and synchronization for the final) Just connect your device to iTunes and pressing the SHIFT key (Windows) or Alt key (on Mac) and click the UPDATE button to select the IPSW file of iPhone iOS beta 6.
When you restart the device can restore from backup to recharge your custom settings.