Unlocking means that you can use it on any carrier. You can actually buy unlocked iPhones from Apple, just not in the US I believe. It was jailbreaking, the act of adding thrid party app stores and features that was once bricked.
You should be fine.
They never have bricked phones after an update... whoever said that was a paranoid fool.
That's not totally true. The update in late Sept. 2007 caused iPhones unlocked back in late-August, early Sept. 2007 to stop working and this was an unrecoverable issue (phone was totally dead) until Apple updated the baseband sometime in early 2008. But since autumn 2007, there have been no updates that caused unlocked iPhones to brick.
That sounds more like a bug than a deliberate attempt to shut phones off though.