Here are a few methods to save power and extend talk time on your iPhone.
Saving the iPhone's Battery
The 3G capabilities for the iPhone increase the quality of your conversations as well as offering you a relatively fast online network. Shutting of the 3G network can double talk time and save battery life all around the board, if that is the trade off you want to make. The iPhone has a simple way for you to disconnect the 3G network if you want, and to make other changes to conserve battery life.
Shutting Down the 3G Network Connection
On the first application page on your phone go to Settings and then go to the General settings option. In the General settings tab go ahead and tap on the Network option in the middle. When the Network option opens up the very top of the screen has an option called Enable 3G. From here you can turn the network off and on by hitting the button to the right, and then it will tell you the status of the network.
How Bad is the EDGE Network?
By shutting off the 3G connection, your iPhone's ability to download pages and information quickly may make things difficult on your phone. However, it is easy to repair it if you can't stand the slowness of the EDGE network. If you do decide to run on the EDGE network, keep in mind that it will be noticeably slower. The EDGE networks tends to run at 2.5 to 2.7 G so while you may experience slow load times, you'll save your battery so you can keep going for that extra day or so.
Another great way to save battery life is to turn off the automatic Wi-Fi connection. To do this you go back to the Settings option on the first page and select General. From here select Network, and then go to the bottom of the screen and select Wi-Fi. Once here you can go ahead and turn off Wi-Fi at the top and “Ask to Join Networks" at the bottom.
Stop the Pushing Data Option
You can also opt to turn off the “push" option where data is updated on your phone automatically. The phone gives options to do it every fifteen minutes, every thirty minutes, once and hour, or manually. The less often it does this the less battery it takes. To turn it off all together or to change the option, go to Settings and then Fetch New Data. At the top of the screen you will be able to turn push off or change the interval at the bottom.
If you're not on your iPhone every hour, then there really is no need to have data and emails sent every 15 or 30 minutes. Keeping it to once every few hours should help you save your precious iPhone battery.