I might be half retarded pls help. iTunes login relaTed Q?

[evasivenotraKcs]

Okay. I just copped a second hand 3GS and know little bout these phones, as this is my first one. Since I can slide to unlock and set up my home wifi the phone is unlocked? Or is it just activated?
Also, when I hit the app store and dl an app, it has the prev owners login and password, how do I fix that?
And lastly, I plan to put this phone on tmobile. It's running ios4.0, I doubt the prev owner JB it does that matter for putting it on tmobile?

[Turnamental]

You got a long way to go to get it jailbroken. It depends on what bootrom is has on the 3Gs. Must be a "first run" 3Gs.

As far as the iTunes login goes... There is a place in "settings" where you can login the Apple login. Change it from the previous owners to your own.

[evasivenotraKcs]

Yeah I have basically deduced that since it is on 4.0 without me having Updated it from 3.x.x and saving blobs, whatever those are exactly, I am going to be waiting for someone to drop a new jailbreak, unless I can somehow DL and downgrade to the 3.1.3 firmware From here which I understand as it's not possible that way.

So can I just drop a tmobile sim in at this point and roll? Or do I have to wait to jailbreak and unlock still? Thanks for the helps.