Upgrading unlocked iphone 3GS running on 3.1.3

[iphonestar]

Hi,

I have a US AT&T unlocked Iphone 3GS running on ios 3.1.3 and baseband 05.12.01. I would like to upgrade to the latest ios5 to take advantage of the icloud functionality. I am currently running my phone on O2 network and I don't have the original AT&T sim. Is it possible to do this currently or do I need to wait for some time ?

Thanks for your help !

 

[iphonestar]

Hi, Is there any update on this? Thanks

 

[neo_gr8est1]

For this you will need a custom iOS5 firmware. You can get this using redsnow but only on a Mac; or snowbreeze for windows. Jailbreak using either of the two and then unlock using ultrasnow...

Im a windows user and personally waiting for the Redsnow functionality on Windows... But the above method should work fine...

This should help:
Jailbreaking iOS 5: Status Update