5.15.04 unfortunately, also I checked the boot loader version and it wasn't the rare/early one that allows downgrading the basedband. But, i've just got my unlock message from O2, and it's unlocked great and my 3 sim is now up and running 
given an iPhone 3G, advice please
- Thread starter davethe11
- Start date
It is, yeah. You have to shift-click 'restore' in iTunes and point it to the firmware file. Then the phone will get stuck in recovery mode after the restore - you need to download a program called RecBoot to kick it out of recovery mode.
Downgrading wipes everything from the phone, so make sure to back up first!