Right now my DVD Jon' activated iPhone works both ways. Logic would dictate w/o SIM battery life should last longer, but I am beginning to think it may actually last longer when the sim is in there. Anyone have experience one way or the other? Thanks a lot. I figure every little bit helps long-term before I need to get it reconditioned by apple

I don't know which is better, but you can switch to "airplane mode" to turn off both Wifi and Phone to save power. I do that when I'm just using iPod features.