Share your experience!
Can you first check if the same occurs in safe mode?
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008
If you experience the same while on safe mode, it'll be wise to repair your phone with PCC
Bridge (for Mac)
Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
Hi dhaval411,
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Are you using a case or screen protector? if so they may be to close or covering the Proximity sensor which would cause the screen to stay black whilst on a call.
Let us know how you get on.