How can someone leave a non-existing number on your display phone?

Question

Christmas night, came home to find a number on display. Called it back over the next few days and it is dead! Thinking it was a friend I went through all my indexes...not there. Went online and found that the number doesn't exist...and there is no such code either! How can someone do this? Could it be from a prison? I know they have the security thing. Thanks for any light you can throw on this.

Answer 1

maybe the number used is that from a phonecard

Answer 2

Usually they are sales calls or telemarketers..