Sounds like a file is corrupted somewhere. You may need to do a full restore, without restoring from backup... If you restore from backup, its just going to sync it back up to the phone..
Sometimes the files just get bugged up a bit. Was there any reason you were on the previous firmware for so long? Keep in mind, if you don't restore from backup, you will lose everything.. So make sure you are in sync with your computer..
So you're saying you've always had this problem? It's unfortunate that you had to unlock it, because otherwise Apple would've been happy to fix it for you.
now what should i do.. ??
i am not able to use the phone to the fullest and always worried while answering the call too that it will turn off anytime...