I have an iPhone 3G.
It is my phone (not a contract) on Telefonica O2 and supplied by them from new. It is on an O2 Simplify monthly tariff.

It is 05.15.04 & 4.2.1 (8C148).

I have backed it all up before doing anything.
I have six SHSHs from TinyUmbrella.
I have just pwnaged it on my Mac.
I did not touch the baseband as its not contractually locked to O2.
After many hours ( I had to take the .ipsw and install using iREB on Windows 7) I find I have a decorative Jailbroken paperweight. It all works but no carrier/phone signal.

I have no carrier so I phone O2 they tell me the iPhone is locked to O2 via baseband 05.15.04. They immediately requested UNLOCK code to send me and apologise (sort of).

When I get the UNLOCK code I will have to connect via iTunes, enter code and thus unlock iPhone from Telefonica O2.

Will this UNLOCK process effectively restore the phone carrier/3G function with no further intervention ?

Will it change the baseband from 05.15.04 to XXX ?

Will I have to restore iPhone 3G to pre-jailbreak state before UNLOCK process with iTunes ?

I did not upgrade my baseband 05.15.04 to the iPad 3.2.2 - 06.15 as I didn't think i was locked in by Telefonica O2. Also this upgrade seems to be a dangerous point of no return.

All advices gratefully received.

Thanks

M&C