Talk:Ringback number

Additional information on special phone numbers
The following information is not reliably sourced, but is interesting:

Ringback numbers that produced as a side effect another dialtone instead of a tone and a connected circuit seem to have been discontinued or changed from a short code to a regular-length number at a distinct point in time.

In most instances you must call the ringback number, quickly hang up the phone for just a short moment and then let up on the switch, you will then go back off hook and hear a different tone. You may then hang up. You will be called back seconds later.

A current loop is a low-impedance DC circuit (frequently powered at 24 volts) that carries audio as amplitude modulation. A loop, though, is a test number used by telco employees:

Loops are a pair of phone numbers, usually consecutive, like 836-9998 and 836-9999...When BOTH ends are called, the people that called each end can talk through the loop.

A dead battery is a now-obsolete special calling number that would connect to a normal DC-powered circuit with no modulation. I'm not sure they exist anymore.

There used to be numbers that would give you a connected line with an audio tone. They were used instead of tone generators or electrical buzzers to trace lines from the street to a house or within a house.

There are some numbers that always answer as busy.

There are some numbers that temporarily disconnect phone service.

Section References
The above references were added on March 18, 2010. When checked on April 21, 2020, they were all dead links.--Thomprod (talk) 12:27, 21 April 2020 (UTC)