What to do if the call answering keys are not working on my Lumia 620 phone?

Call answering keys may not work properly if one or more your fingers are touching the display when the phone starts to ring. When this happens, the call answer and call end keys are grey and do not function at all, and the call can’t be answered or ended. Also the call answer by sliding your finger doesn’t work in this situation. You can fix the problem by pressing the lock key twice.