Read the tips for extending battery life on apple Web site. Apple describes the tips as "commonsense pointers." well, they're actually blindingly obvious to anyone with any technical knowledge. But of course, many of Apple's users are technologically unsophisticated, so they can use more help. And a couple of the tips are useful even to power users.

Unlike other smartphones, the iPhone doesn't have a user-replaceable battery so you can keep a fully charged spare or two in your briefcase.

Acctually, do have a few options You could try and maximise it, or you could pick up some battery packs like the iPhoneck. Sure it extends your iPhone 3G by a whopping 2-inches, but it can also fully charge your phone in 90 minutes. There is also the older FastMac iV and the Kensington Mini which should both work fine with the 3G.

Another tips is Lock your phone when you're not using it, to be sure that nothing happens when you touch the screen. And i hear charging the battery to 100% and then completely running it down will give best result too.