is my z550 done?

to make a long story short, i was given an unlock code by t mobile to unlock my Suncom branded z550, however it was the wrong code and it failed 5 times and will let me type in a code now, but says "not allowed" now. Sony told me it was forever locked to Suncom now which i dont beleive. Suncom dont exist anymore, so how do i begin to fix this situation? i dont mind reading if someone will let me know if its fixable and what do i need to read? i am new but not totally dumb:)! thanks 4 helping. jj

**im sorry, i am with t mobile now and i want to use the tmobile SIM. this phone will only accept a suncom at the moment. i may not have been clear.

you need to unbrand it and unlock using patch

ok i tried to unbrand it. i d/l the necc. files and when i clik flash and hold down "C" it dont do crap? i followed instructions from one of the sticky posts, but i cant get it to flash? i load the files in lite 1.11, then i clik flash, then i hold down "C", then i plug my phone, and it does nothing? the green status bar just goes and goes for minutes? am i doing something wrong? should my sim be in or out? my phone off i presume?

Did you installed USB Flash Driver ?
You don't need to unbrand it in order to unlock it. Just use this tutorial:
A. How to apply the generated patches to DB2010 CID49 phones