The Samsung Supersonic is most likely a code name used for the upcoming Samsung Vibrant. The Vibrant is the T-Mobile version of the Korean based firm's Galaxy S, and the pricing would seem to fit in with the theory that the Vibrant and the Supersonic are the same. The price is $199.99 after a $50 mail-in-rebate and a signed 2 year contract. Off contract, the price is $499.99. The Vibrant is expected to be available for pre-order today (Thursday) at Radio Shack by purchasing a $50 gift card which gets you an appointment on launch date, July 21st. After you purchase your handset and set yourself up with a data and voice plan, you will receive a $50 gift card in the mail from The Shack. You can also pre-order starting July 1st at Radio Shack's online store at this link.
Samsung Vibrant Preliminary Specifications | Hands-on
source: TmoNews, RadioShack