Im going to be getting an iphone in the UK as soon as 1.1.2 has been broken. Can I just confirm I need to unlock it as well as jailbreak it right?

My main question is regarding re locking of the iphone. Ive been told that if you connect to itunes with an internet connection itr automatically locks back up again. I was under the impression that only if you flash/update the firmware then the iphone would lock back up again. Can anyone confirm which is correct?

Thanks for taking the time to read this.