Yes i'm JB. 3.1.3 2G iPhone.
Since on 3.1.3 wifi has never worked. I'm going back to 3.0 tomorrow, if it works again its software, if not it's hardware.
I used redsn0w for FW3.0 and sn0wbreeze for FW 3.1.3 ... maybe is sn0wbreeze, but i doubt it.
And I understand how completely "noobish" my first fix sounded, but I'm fairly certain it was either that or dumb luck that fix that got my wifi working. And if you're at the point where you're pulling your hair out over this - connecting to a fake network 20 times isn't going to do any harm ... ... ... to the phone.