How to unlock 3gs temporarily

[hia]

I want to unlock my iphone 3gs with os3.1.2 to use abroad for a month. (I think I should do this with blackrain and cydia/blacksnow from what I've read). My question though is about my return to the US- will I be able to update my iphone through itunes and use it the same as before the jailbreak/unlock? I've read that you can't update the os after unlock or update itunes and I'd like to, so not sure what to do. Advice on any step in this process of unlocking, using abroad, and then returning to use in the US, would be appreciated.
Thanks!

 

[Moi un Mouton]

I want to unlock my iphone 3gs with os3.1.2 to use abroad for a month. (I think I should do this with blackrain and cydia/blacksnow from what I've read). My question though is about my return to the US- will I be able to update my iphone through itunes and use it the same as before the jailbreak/unlock? I've read that you can't update the os after unlock or update itunes and I'd like to, so not sure what to do. Advice on any step in this process of unlocking, using abroad, and then returning to use in the US, would be appreciated.
Thanks!

When you get back, you can just restore in iTunes and everything will be back to normal, phone carrier-locked again