Both Samsung Supersonic and Motorola Charm are upcoming T-mobile smart phone, the Samsung Supersonic is probably the Samsung Vibrant that was announced a few days ago, it's not a name change,  Supersonic is actually a code name according to Tmonews.

The Samsung Vibrant/Supersonic will run you $199 with a 2 years contract.  But $449 without a contract, which I think it's pretty fair considering how powerful the handset is.

Tmonews also revealed the price of the upcoming entry phone by Motorola, the so call Motorola Charm, the phone will only run you $79 with a 2 year contract.  It's another one of the feature phones that targets teens.

source: Tmonews