The 16GB version will be available to purchase online starting July 11 (that's this Wednesday) and will arrive in retail stores by the end of the week. The 32GB version will be made available 'shortly after that'.
The cost of both will be $199.99 (16GB) and $249.99 (32GB) after a $100 mail-in rebate.
So if you weren't able to get your pre-order in or you're just waiting to play with one, you'll be able to pick one up tomorrow and at the end of the week directly from the store. If you do pick one up, share your experience in the Samsung Galaxy S III Forum!