Since I see some dumbasses selling UDID activations for IOS 7 Beta, here is a quick tutorial for how to get it, free of charge, without having to activate your UDID.
First, Backup & Restore your iDevice, and install the latest IOS for your device (6.1.4 for 5, 6.1.3 for others)
Now download IOS 7 Beta (make sure to get the correct one) Here If you don't know which one to get, use This to figure it out.
Now open iTunes, connect your iDevice and hold shift then left click the update button and browse to where you saved your IOS 7 beta and select it.
iTunes will now go about the process of installing it onto your phone.
TA-DA you have IOS 7 Beta, no UDID, no hacks/cracks, and working as normal.
You can sync and download and do whatever you wish.
You can also update to later betas using the Over-The-Air update.