When you slide your phone up, enter this code: *#4777*8665# This will appear on the screen like this: *#4777*—– . Then, a secret menu will appear on your screen. Go to the option GPRS Detach and click it. Next you will have to wait some time, about 3-4 seconds and get the message: GPRS Detach confirm.
Your stand-by time has increased with 20% now!. GPRS detach will also remove the small blue background G on your screen which some people don’t like it. I also advice you to drain the battery completely before charging the first 3 times you charge. There’s no real proof that this will improve your battery life but there are rumors.(do not drain lipo batteries because you’ll harm them doing this.)
Another option is to buy a better battery; the standard battery had only 690mAH while this battery provides 1000mAh so it will increase the stand by time +- 30%. Yet another thing you can do is set the display brightness to the minimum, so the screen will consume less energy. And don’t leave Bluetooth activated, it’s very power consuming!
You should also check the Samsung SGH U600 Tips article.