Carrying the iPhone 3GS is like having a computer in your pocket. The phone lets you browse the Internet, play games and manage calendars wherever you have access to to a 3G, EDGE or Wi-Fi network. All of these activities, however, reduce the device's iphone extended battery life--the amount of time the battery runs before needing to be recharged. A few adjustments can help you get more mileage out of the battery on an iPhone 3GS.