I have an Iphone 5S. When I receive calls I do not see a number it only reflects "Unknown" on the screen. How can I change this to ensure that it reflects either the number or name if the person is in my address book?
If you see "Unknown" this means that the caller is not transmitting his ID (i.e. number) to your carrier and hence your iPhone.
Not much can be changed unless you pick up the phone and ask the caller to change his Caller ID settings on his phone.
In addition, some business numbers and calls over VoIP tend to appear as "Unknown". It is not the fault of your iPhone but from where exactly the call originates.