The difference is whether you want to unlock the iPhone or not. Upgrading to 3.1.2 still provides you ways to unlock the iPhone, however, as far as I know, 3.1.3's baseband will be trickier, or even impossible, to unlock.
In a nutshell, jailbreak can work up to 3.1.3, while unlock only up to 3.1.2.
If you just want to tether, but don't bother unlock. 3.1.3 should be ok for you. At least, that's what I do right now. Not a fan of AT&T, but not against it either.
In a nutshell, jailbreak can work up to 3.1.3, while unlock only up to 3.1.2.
If you just want to tether, but don't bother unlock. 3.1.3 should be ok for you. At least, that's what I do right now. Not a fan of AT&T, but not against it either.
I still have iPhone os 3.0 on my 3GS. Should I keep the os or update before I JB?