There are essentially three avenues to connecting to the internet with the iPhone – EDGE network, 3G network, and WiFi. If you use the cell networks (EDGE/3G) to access the internet most of the time, make sure that you disable WiFi so that your phone is not constantly checking for hostpots (places with wireless internet connections). It only takes a second to turn it on when you actually need to use it. To disable WiFi, go to Settings, click on WiFi, and slide the WiFi setting to Off. This is one of the best ways to conserve your battery life, so if you don't use the WiFi feature all the time, it's probably best just to keep it off.