I have a iPhone 3GS -it has served me well. I'd like to pass it on, so I want to wipe it and upgrade to ios 6. I'm at 4.2.1 with baseband 05.15.04-6.4_M3S2. When I try to upgrade with itunes, it says I'm at the current version. (itunes I did a JB a while ago, so do I need to restore something to allow itunes to recognize the upgrade?

And yes this is a 3GS - 16GB, not a 3g.