i started the process for pre-ordering the galaxy s3 through the VZW portal but had to move to the phone due to address issues.
The person on the phone was helpful and said, several times, that I would not lose my unlimited data plan since I was pre-ordering.
This will probably be a big leap from my Motorola Droid (running CM7.2 stable) which has been a great phone for the past two years! It will be interesting as this is my first samsung phone AND one of the few times I've bought a phone RIGHT at launch. Actually, it was also my first time ordering a phone for myself without having to step foot inside a store.