According to a screenshot which shows the internal pricing of various T-Mobile phones, the Motorola Charm (also known as the Motorola Basil) will cost $149.99, but $74.99 after a $75 MIR. In addition, the same screenshot shows the pricing for a mysterious phone known as the Samsung Supersonic. Apparently the Samsung Supersonic will cost $249.99, but $199.99 after a $50 MIR. The Samsung Supersonic pricing lines up with the Samsung Vibrant pricing, so it is quite possible that the Samsung Supersonic is simply the internal codename for the Samsung Vibrant. Of course, there is the possibility that the Samsung Supersonic is a different phone entirely. Keep in mind the above pricing is for a two year contract only.
In case you want to pick up the Motorola Charm without a contract, the price is $269.99. The off contract pricing for the Samsung Supersonic is $499.99. Hopefully T-Mobile will confirm either the Motorola Charm pricing or what exactly the Supersonic is shortly.