I have a BlackBerry 8300, does it support T-Mobile?

Ya sure blackberry 8300 mobile is compatible with t-mobile sim only if it is unlocked one .Else if the mobile is locked to some other network provider then it wont accept t-mobile sim until you unlock it ..You can easily unlock your 8300 mobile using sites like UnBBLock.com they are rendering unlock code for all blackberry mobile models at reliable cost .After unlocking your phone you can freely use it with any GSM sim ...