Ringback number, a number used by phone companies to test whether a telephone line and phone number is working
Lucky Number Slevin | Reynolds number | Mach number | serial number | Random number generation | International Standard Book Number | prime number | Personal identification number | number | Two in a Million/You're My Number One | Social Security number | Rikki Don't Lose That Number | Prime number | Premium-rate telephone number | Jackass Number Two | Opus number | Number Girl | List of WTA number 1 ranked players | Lah number | Erdős number | Emergency telephone number | Betti number | You're My Number One | What's Your Number? | The Number 23 | The Murderer Lives at Number 21 | Ringback tone | real number | opus number | natural number |