you guys ares very clever at all kinds of stuff so i thought i might see if your wisdom stretchs this far.

I have a new iphone that i think is locked to a particular brand SIM. (its supposedly from the US). So i want to unlock it to get my O2 sim from my other iphone in there and get it working.

Is this possible without jailbreaking it?

if not, how does one go about jailbreaking it, and is it possible to un-jailbreak it later for whatever reason?

No, I don’t think there is anyway to unlock a non-jailbroken phone. But I’m pretty sure it’s legal these days.

I jailbroke (jailbreaked?) my 3G using Pwnage tools, and I think UltraSn0w. Search for it (iPhone dev team), there’re are too many variables depending on what model, firmware and baseband you are using. There are also other unlock tools available, each for different situations. For me, it was pretty straightforward…

HOWEVER, do read up a lot before you do anything. If it’s a new phone running the latest iOS, then the baseband may be too high for the unlock to work, and jailbreaking it won’t help.

You can restore back to a non-jailbroken iOS by using a custom restore through iTunes. Be very careful about not doing a ‘normal’ restore from iTunes, as this may lead to the baseband problem above. I’d also read up about how to save your SHSH blobs through Cydia; I’ve not used them but I read that it was pretty important to have these.

Hope that helps

O2 will unlock your phone free if you are on contract with them. I did it once before and all you do is fill in an online form and they send a text when its done. However, I just got a text saying they can’t do it with my current model – haven’t found out why yet!

Yes you can unlock without going down the jailbreak route.

O2 will unlock your phone free…

… if it’s locked to O2. The OP’s problem is that the phone is locked to some US company (who’d have to do the unlock).

Yes you can unlock without going down the jailbreak route.

Didn’t know that – got any more details?