This automated service “listens” to check for Ringback tones, Busy Signals, Answered call, Voice mail automated answering, or network operator injected messages such as “the number called is not in service”.
telephone | Telephone tapping | Plain old telephone service | Nippon Telegraph and Telephone | 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 | Telephone exchange | telephone exchange | Social Security number | Rikki Don't Lose That Number | Prime number | Premium-rate telephone number | Jackass Number Two | The Bell Telephone Hour | Telephone switchboard | Telephone company | Telephone | Opus number | Number Girl | List of WTA number 1 ranked players | Lah number | Erdős number |