Should I update my iPhone 4 (4.1 to 5.0.1) or stay outdated? NEED HELP, PLEASE!!!!!!?

Question

Ok, I know that this may be long but bear with me, really need your help guys!!!!
Ok, so a few years ago, I bought an iPhone 4 (I was in Zimbabwe, now in the US) that was factory unlocked from what I can tell. Reason why I "THINK" it's unlocked is because
1. It did not have Cydia installed when I got it, just stock with native apps only
2. Running on 02.10.04 Baseband (That cannot be Cydia Unlocked), I manage used several Network Providers and all Sim cards worked and still do, no problems. (Using T-Mobile Now)
3. Model Number is MC603B, and according to my research, it is a factory unlocked model.
Unless im mistaken???????
Here we go. The iOS 5.0.1 is out and I am now running iOS 4.1 (Jailbroken), which is really bakward, so loads of tweaks and apps cant run on my outdated iOS and i want iOS 5. I have heard people all over the internet complain that after the iOS5 upgrade, their phones locked-up and can't dowgrade or activate after the update, so if that happens im STUCK forever, and I really dont know what to do!!!!
HERE ARE MY QUESTIONS:
1. Is my phone really factory unlocked, based on what I listed above? Or is there any other way of checking???
2. If I DO update, do I risk locking-up my phone????
***3. Should I update it "while preserving my baseband" and still manage to Activate it, or just leave it to update my baseband????? PLEASE HELP. Read my questions carefully and answer on what you think.
Thanks alot guys

Answer 1

Well, since the iPhone is not officially sold in Zimbabwe, & that's where you purchased it, you can pretty much count on the fact that it was hacked to unlock it, regardless of what you think or see. Thus, you can be pretty much assured that if you update software your phone will be re-locked to the carrier it was originally locked to.