So back when I had a simple flip phone one of the features you could do was... set a custom ringtone for an individual and also set a ringtone for all in your contacts that don't get that custom individual tone and then finally you can set a tone to anyone who is NOT IN YOUR CONTACTS.... So I have a bunch of custom tones for friends and family and then EVERYONE else gets the tone I set for my ring... But i want a tone for those not in my contacts so I know they are not. Flip phone did it.. Iphone does not, as far as i know.