Can i update iPhone 4 to iOS 6 and still be unlocked?

I bought the iphone 4 with a 2 year contract from AT&T and now that my contract expired i asked att to unlock it for me and they did. My question is can i still have the unlock, to be able to use on tmobile, after i update it. I do have my iphone jailbroken but i did NOT unlock it through a hack or jailbreak i asked att to unlock it. My iphone is running a little slow due to how many cydia apps i have and i just want to start fresh. I don't really care about having it jailbroken anymore. I'm fine just as long as i can us it regulary on tmobile with MMS and Internet.

It really depends on how it was unlocked. How did AT&T do it for you? What did they tell you to do?

If it's a software unlock, then you're going to "re-lock" when you update.

if you need to unlock any generation AT&T iPhone you can go here: http://gsmunlocklabs.com/unlock-iphone/

it's a permanent unlock and you'll never have to worry about it again when you go to update your iphone.