Iphone 4 unlocking and forgotten password?

This is gonna be long but thanks for reading and answering
So about the time the iphone 4 came out my mom somehow got it at a phone store they said they would unlock it but never did (this was before apple when apple was only with att) we were basically scammed i guess
but i didn't really care much i just used it mainly as an (expensive) ipod. I jailbroke it and it was awesome haha i loved it but then i guess the battery died (it would turn off if it wasn't connected to the charging cable) and i didn't realize it then so i kinda just threw it off to the side for two years until a few months ago when i tried to play with it and then my stupidself forgot the password since it was just off for two years and i kept on trying to figure out the password and it was basically locked for eternity so i tried to restore it and there was like an error i think it was like error009 or something and now it is stuck in recovery mode and this guy wanted an iphone for cheap so i decided to try fixing it up for him
i just bought a new battery to change myself and after doing that i'm hoping the restore will work
i've never used att as a carrier so i don't know how to unlock an att iphone 4 to t-mobile? And i don't want to jailbreak it again so is there anything that i can do to unlock it with out paying a website or taking it to a shop?
thanks
i also use tmobile by the way

Added (1). its been two years since i bought it from the store so i doubt that theyll do something about it but ill try calling them up as a last resort if i can't unlock it myself

It's easily fixable, first you have to update your iTunes on your computer along with the drivers (if you require them) then you pluck you iPod in and restore it's that simple the error is more that likely to be a clash between higher and lower versions of ios so they arent compatable