For all previous GMs, there has been no need to do anything special (register as a dev, give your UDID, jailbreak, etc.) to install it on an iPhone. I've installed each of the GMs from 3.0 on my iPhones with no trouble whatsoever, and simply updated to the x.01 or x.1 when available.
OTOH, I've never installed any of the other betas, nor would I; I'm not a developer, and I only use/keep one iPhone at a time. I need it to work consistently, so I wait for the GM, but I am too impatient to wait until it's released to the general public.
HTH