1. Copy /System/Library/Carrier Bundles/Unknown.bundle/carrier.plist in your computer.
2. Open it in a plist editor(i use plistedit pro for macbook) and then go to operations and then change format select XML format
3. Change t-mobile strings with the carrier strings that shows in your phone(in my case it is IDEA (India) so i changed t-mobile with IDEA)
4. Once done go back to operations and then change format to Binary.
5. Upload and overwrite the original file including your modified .png's
Restart your phone and you should be fine.
I tried most methods mentioned in fourm but non worked so I assume this is meant for non-AT&T users and countries where following are not applicable.