I have just inherited a Galaxy S Captivate (ex US At&T model of Galaxy S) and it is currently "unlocked" and so will work with any NZ carrier. I don't really understand what this unlocking business means and want to know: If I install the latest iteration of Android on this phone (which a google search revealed can be easily done via a PC by downloading Kies Mini), will I "re-lock" this phone rendering it unable to connect to NZ networks?

It is currently running 2.2 Froyo and would like to upgrade to 2.3 Gingerbread.