Unable to dial numbers while on another call

[pais]

Unable to dial numbers while on another call. The number gets dialed but is not visible while on another call

[_alexdon_]

Can you 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

[pais]

Reboot in safe mode did not work for me.

I tried dialing the number when on call (in safe mode)

Even then the numbers are not visible when dialed during on call

[_alexdon_]

This is strange,I have seen the same problem with someone and in safe mode it worked fine. You could perform a software repair.