Danger Hiptop 2 / Sidekick II

if I unlock the phone to use with my Cingular SIM card, but I sign up later for the Sidekick Data Plan? I've heard that the programs specifially designed for T-Mobile will be lost or unavailable. I want to unlock my Sidekick, but when I do sign up for the Data, I don't want it to be all messed up. Especially since I have the Mr.Cartoon version..and there's no warranty on it..

Thanks