The user-accessible screws on the new iPhone 3G might be an indication of user-changeable batteries. (although we highly doubt Apple would do that)
As previously noted, Apple’s new “guided tour” of the iPhone 3G demonstrates operation of the AppStore and a slew of already-detailed functionality. Closer inspection of the video has unveiled a few more revelations.
A look at the bottom of the new iPhone 3G during the video reveals new audio components on the bottom of the iPhone 3G. The left side grill is the speaker and the right hand side is the microphone. Apple purports “greatly enhanced” audio from the new hardware.

Other interesting stuff at Zedomax.com: Apple, audio components, Batteries, battery change, guided tour, hack user, iPhone, microphone, new hardware, revelations, screws, slew