Unavailable

There are two reasons a number would not appear.  If a subscriber is paying to have his/her number hidden from the public, the number would appear as Private.  Although I've also seen Private Number, that may have been a spoofed (fake) entry.

Unavailable would appear if the call is from a system where Cox can't retrieve the number, such as overseas calls, calling cards or some calls routed through switchboard systems (hospitals, university dorms, etc).  Since computers can now make telephone calls, Cox also can't retrieve numbers from those computers.

Computers are the greatest problem nowadays.  Scammers use computers and concoct fake numbers with phony area codes and phony exchanges.  It seems you can't trust any number you do not recognize.  Everything on my caller ID could be fake.

Be safe!