TAD meaning in Telecommunication ?

An answering machine, answerphone or message machine, also known as telephone messaging machine (or TAM) in the UK and some Commonwealth countries, ansaphone or ansafone (from a trade name), or telephone answering device (TAD), is used for answering telephones and recording callers' messages. If a phone rings a number of times predetermined by the phone's owner, and nobody is present to answer the incoming call, the answering machine will activate and play either a generic announcement or the voice of the person being called announcing that nobody is able to come to the phone at the moment. Following the announcement is a beeping tone which prompts the caller to record a message after the tone concludes.

Unlike voicemail, which can be a centralized or networked system that covers, and mostly extends, similar functions, an answering machine is set up in the user's premises alongside—or incorporated within—the user's land-line telephone. Unlike operator messaging, the caller does not talk to a human.

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