here i will show you how to enable battery percentage indicator like iphone 3GS OS 3.0
If you are looking for the battery percentage toggle in your 2G/3G iPhone running on OS 3.0, stop looking cuz it's not there! Apple seems to have left this feature for the 3GS exclusively!
However, there is a way to enable it:
1. First you need to Jailbreak your iPhone, use PwnageTool or Redsnow check the dev team blog. (if your iphone currently running OS 3.0 just go step 4)
2. Download the M68AP.plist file from the link:
http://www.4shared.com/file/113188452/9434236e/M68AP.html3. SSH into your iPhone. (Or use iPhoneBrowser 'look it up in google its right there!)
4. Go to /System/Library/CoreServices/Springboard.app/
5. Replace the M68AP.plist in the directory with the one you downloaded
6. Restart you iphone.
7. Now go to the application Settings -> General -> Usage and there will be a Battery Percentage toggle and you can use it to enable battery percentage next to battery icon in top-right corner.
http://www.yaznewish.com 
I have the percentage next to the battery icon via sbsettings 3.0...