Answering machine

As landlines become less important due to the shift to cell phone technology, and as unified communications evolve, the installed base of TADs is shrinking.

Ludwig Blattner promoted a telephone answering machine in 1929 based on his Blattnerphone magnetic recording technology.

[10][11][12] Another commercially successful answering machine was the Ansafone created by inventor Dr. Kazuo Hashimoto, who was employed by a company called Phonetel.

James P. Mitchell displayed a working prototype of a digital outgoing message with a taped incoming system at an Iowa State University VEISHEA engineering openhouse in April 1982.

In some cases the terminal equipment answering a call just sends a slightly modified ringback tone to the caller, while processing the protocol.

Voice signals may simply be captured to and replayed from analogue media (mostly tapes), but later TADs shifted to digital storage, with all of its convenience for compression and handling, for both the greeting and for the recorded messages.

This holds especially for the TADs with digitally stored greeting messages or for earlier machines (before the rise of microcassettes) with a special endless loop tape, separate from a second cassette, dedicated to recording.

There have been answer-only devices with no recording capabilities, where the greeting message had to inform callers of a state of current unattainability, or e.g. about availability hours.

On a dual-cassette answerphone, there is an outgoing cassette, which after the specified number of rings plays a pre-recorded message to the caller.

Some machines also allow themselves to be remotely activated, if they have been switched off, by calling and letting the phone ring a certain large number of times (usually 10-15).

Some service providers abandon calls already after a smaller number of rings, making remote activation impossible.

This refers to analogue sites, which support voice, fax and data transmission via landlines by adhering to specific protocols established by the ITU-T. Any incoming call is not identifiable with respect to these properties in advance of going "off hook" by the terminal equipment.

Besides these solutions, mostly requiring a constantly running computer, since a wake-on-ring function then (~1995) started to take too much time to boot up an operating system, a few so-called selfmodems were available from e.g. USRobotics or ELSA Technology: the Sportster MessagePlus, the 56K Message Modem External, and the MicroLink Office.