Apple rates the iPhone 3G's talk time at 5 hours over the high-speed 3G network. While the call quality seems vastly improved due to more data being passed through the 3G pipe, some of the more chatty among us may find that 3G isn't just fast -- it's non-user-replaceable-battery draining fast!
Don't care as much about speed and clarity as you do sheer volume of talk time? Or what if you're just in an area that's not (yet?) covered by 3G? You're in luck! Apple has provided a way to turn off the 3G -- and blazing fast broadband-like HSPA speed that goes with it -- and drop back down to 2.5/2.75G -- and the dial-up-eque EDGE that is turtle to the 3G hare.
Boom! 10 hours of talk time! (And for those of you in countries with more restrictive/ridiculous data caps, a way to help pace yourself and starve your data-hungry iPhone).
Just remember: slow data transfer, not as good call quality, no simultaneous voice and data (you can't talk and surf the web on EDGE at the same time).
Step-by-step instructions after the break!