The new iPhone 3G S is available for pre-order on the Apple Store. So there is no need to camp in front of an AT&T store on June 19th. You just can order it now and wait until Apple ships it to you for free actually.
In a nutshell the new iPhone 3G S is 2x faster, has a 3MP camera, voice control, HSDPA, Digital compass and also comes in a 32GB version. The new iPhone 3G S comes pre-installed with iPhone OS 3.0, which was released two days earlier on June 17th.
The new iPhone 3G S 16GB sells for $199 and the 3GB iPhone 3G S sells for $299.