I have a iphone 6 with latest ios. but when other people call me, the first time always not available before the ring tone. When they call me again, the phone is nomal. I have missed quite a lot of calls.
The symtoms are :
Someone else call me
they have 'the number you dailed is not available ' voice messge
I have the missed call notification
They redail and my phone rings
I have update the ios and also tried reboot the phone but issue still exists