how do I take my iphone 3gs off of demo mode

Demo mode?

Connect it to a computer with the iTunes account it is tied to. Then do a restore.

atormey wrote:

like when it is in the store and showes all the apps. it has random contacts and will not let me set a passcode or move icons

I have never seen this. I don't remember seeing it in the manual either.

iPhone User Guide (For iOS 4.2 and 4.3 Software)

I've seen this before. A restore will not restore the phone to a stock iOS, certain things will not be available. Your best bet is to return the phone & get your money back.

I've told you what to do, you will never be able to put a stock iOS on that phone. Demo iPhones are designed to prevent users in stores from totally screwing them up...certain functions are simply not available & there is no way to fix this(at least that I'm aware of).

The software(firmware) on your phone. Your phone has a special version of the iOS on it called "Demo Mode".

what if you downloaded an ipsw for it then restored from that?

Did you read all of wjosten's posts? He already said that doesn't work.