Unlocking a tmobile phone??! Please help!?

I would like to get a tmobile sidekick but i have at&t. does anyone know anything about unlocking those? I know that there is a thing called sim unlock, but i have no idea what it does or how it works or if sidekicks would even work with it. thanks so much!
oh and is it legal?
Does the sidekick ID have a camera?
and do you have to be a tmobile customer and have a plan with them to get the phone even if i'm not going to use their service?

well as a tmobile worker we dont notmaly unlock sidekicks because a sidekick is a soft server basically meaning that all your contacts callender events email aim etc. are stored on the danger server so if you lost your sidekick and called for a replacement you put in a sim cars typein ur email username and password(for tmail) and all your things will be back on (this is great if someone steals it then you have things they put on it) and the sim card is just basically saying hey this is me im a sidekick and the danger servers identifies it on tmobile...if tmobile decides to unlock it which they normally dont do. if you put an att sim card in it its not a tmobile sim card and its saying het this is a sidekick and im looking for the servers(on att's network, which they dont have) and that will result in countless errors and network faliures because the sidekick constantly looking for and backing up information on their servers....if you ever put a sidekick and add a new contact or log on aim, send and email or just anything, sit by a speaker (if you have a tmobile sidekick plan) and you will notice the interferance with the speaker and thats all the data its sending to danger and it wont do that with att

plus if you enter contacts in the phone and you forget to charge your phone and the battery dies it will erase everything on your phone

in the end its a bad idea to unlock a sidekick and bring it over to att....ask ant tmobile rep and they will tell you the same thing...and if you did get it unlocked all you can use is the phone for is calling and texting , not the aim email and internet

ps: get a good phone you want from att and then unlock the sidekick because you will find that it is worthless

and unlocking phones is totally legal there is a law and its in out manuals idk what code it is but im shure you can find it on the internet

ooh and the sidekick id does not have a camera and you dont have to be a tmobile coustomer to buy a sodekick...it will be more expensive if you buy it retail so buy it prepaid then it will only be $150