after updating my xperia j (st26i) from ics to android version 4.1.2 , the phone automatically restarts and this only happens when i am on a call and after 30 to 45 seconds it comes back to its normal mode(the call is disconnected).
i have not installed any apps which could cause this problem and the problem was not solved even after repairing the phone.
This seems to be an old or faulty SIM card, get a brand NEW sim card, even if it has been working or if it works on other phones, trust me, just get a new SIM card.
new sim card did not solved the problem , upgrade version 4.1.2 has many bugs, only solution is an update in 4.1.2 android version and testing it before rolling it out and TRUST me it will work.
