Will IMEI unlocked affect upgrading iOS on my iPhones - 3GS & 4S

[ChinaDoll13]

I have my iPhone 3GS probably IMEI unlocked by Fido after I paid $50 for the service.

I was running iOS 5.1.1 when the phone was unlocked.

Now, I am considering upgrading my phone to iOS.6.0

Will the iOS upgrade get re-locked my phone?

What about a complete reset my phone to factory setting ?.... as I am giving it away to a relative and want to clear out everything on the phone....

Will that re-set the IMEI to lock again?

I am getting a used iPhone 4S from my friend.  She told it is factory unlocked.

Is there anyway I can find out if it is probably IMEI unlocked from Apple database?  Who and how can I find out?

I am not sure who was the service provider she original got the phone from. 

Same question on the 4S ... if it is IMEI unlocked ... will upgrade iOS affect the IMEI unlock?

I am scared to upgrade my phones iOS if they will get re-locked.  I need the phones for global travels.

HELP ...

THANK YOU. 

***Edited to add labels***

[LucidEvening · Accepted solution]

This is the beauty of having a hardware unlocked. Essentially, Apple removes the IMEI number from their "Locked iPhone" database and the iPhone is capable of running any iOS version - remaining unlocked. So upgrade to iOS 6 and you'll still be unlocked.

As for telling if your friend's iPhone 4S is factory unlocked, try putting in a different SIM that what your friend was using to confirm if it can run any other SIM. Again, you can upgrade iOS 6 with no affect on the unlock. Upgrade iOS only affects software unlocks, which I cannot comment too much on or this post will be modified or deleted by Fido Mods.

[ChinaDoll13]

Thank you very much .... When I talk to my friend again, I will ask the necessary information.

[LucidEvening]

No problem, that's what the forum is for!