Finally!!!
I have just gotten the email from AT&T with unlock code!
Firstly, My friend submitted and opened the case for the unlock code for me but unfortunately, he did not get any reply from att for more than 3wks.
Fortunately, I found att unlock website could figure out my phone's IMEI and I asked to my friend who has att account with really good stand!!
It took 3 days and the phone works perfectly!! Love it!!!!
Do not open the case if you do not have att account. They do not help you for the code.