WHAT IF WATSON HAD BEEN OUT TO LUNCH when Alexander Graham Bell made the first phone call, in 1876? Bell’s invention let people converse across long distances instantaneously, but not with someone who wasn’t home. That would be the weak link in the communications revolution.

In 1898 a Danish engineer named Valdemar Poulsen patented the first magnetic recorder, the telegraphone, which recorded sounds on a spindle of steel wire. Starting in 1903 he marketed a modified version of the machine in the United States as a tool for dictation and automatically recording telephone messages. After being activated by the signal for an incoming call, the telegraphone recorded the transmitted electrical impulses directly onto the wire. Only when the user played the message back were they converted into sound. Since there was no outgoing message, callers had to know when the machine was in use. The telegraphone could also record both sides of a telephone conversation, with or without the knowledge of the party at the other end. It didn’t work very well. The recorded messages were often incomprehensible, and the steel wire, which had to move across the recording and playback heads at a rate of several feet per second, tended to jam. The American Telegraphone Company went into bankruptcy in 1915 after selling only a few hundred units.

Thomas Edison came up with his Telescribe in 1914. It recorded telephone conversations on wax phonograph cylinders, which could be reused by shaving the wax coating to erase old recordings. It is not clear whether the Telescribe had any provision for answering the telephone when the user was not present. Apparently few businesses returned calls from Telescribe salesmen, and although a number of models came on the market in the following decades, answering machines remained rare and expensive curiosities until the 1950s.

Then U.S. companies began selling and leasing a new generation of machines incorporating the latest advances in postwar electronics. AT&T’s Peatrophone, introduced in 1951, occupied a metal box about the size of a milk crate and used two phonograph turntables for incoming and outgoing messages.

By the 1960s magnetic tape had largely replaced wires and disks in recording devices, and transistors had supplanted clunky vacuum tubes. Lower prices and improved reliability expanded the small market for answering machines at the dawn of the 1970s, but they still weren’t cheap. Top-of-the-line machines cost $800 to $900. The customers for them were mainly small businesses that couldn’t afford receptionists and upwardly mobile people who couldn’t afford to be without high-status appliances.

In basic operation, answering machines of the 1970s differed little from the computerized models of today. Like a telephone, an answering machine has a detector circuit that waits for a ring signal from the phone company. Instead of activating a bell, the detector circuit waits a certain number of rings and then automatically closes a circuit between the answering machine and the phone company, signaling an “off-hook” condition, which is the phone company’s cue to open a voice connection with the caller. A greeting is played, followed by the beep. Unless there is a fixed length for messages, circuitry enables the machine to hang up when it receives a disconnect signal from the phone company or after a long interval of silence.

Even the better models 25 years ago provided a host of inconveniences. Installation could be tricky, with phone companies requiring an expensive coupling device designed to prevent third-party equipment from damaging phone lines (or from competing with the phone company’s own equipment). You could get around this by using answering machines that didn’t plug right into the phone line; instead the telephone handset rested in a cradle, like an early computer modem. Sound quality in these models was poor. Many machines used built-in tapes, inaccessible to the user, or special tape cartridges available only from the unit’s manufacturer. Cheaper models economized by using the same tape for incoming and outgoing messages and making the user record a separate outgoing message for each incoming message, taking care not to erase the beep accidentally.

Still, the benefits outweighed the hassles for those who could afford a machine. In 1973 Alvin Toffler, the alarmist author of Future Shock , observed the rapid proliferation of answering machines with apprehension. Their surging popularity, he fretted, was giving society little time to “make the subtle kind of adaptation necessary to it before it has committed itself to the use of the technology. Maybe the consequences are trivial. But who knows and who asks? Nobody.”

Answering machines could undoubtedly relieve owners of the nagging worry that they might miss important calls, but for the people making those calls, being greeted by a recording rather than a live person was sometimes unsettling or even alienating. One 1975 magazine article advised consumers to try to come up with a greeting that would get the caller through the “shock of his discovery as gently as possible.”

In the 1980s lower prices and increasing experience with the concept of talking by phone to a machine opened the way for answering machines to become standard equipment for young urbanités. Sales quadrupled between 1982 and 1986 while the average price for a unit dropped below $100. Modular jacks and the removal of phone company constraints made installation simple; touch-tone codes provided an easy way to retrieve messages on the go. Alvin Toffler’s fears fell by the wayside, and suddenly callers began to be affronted when someone didn’t have a machine.

WITH BARE-BONES MODELS COSTING AS LITTLE AS $19.95, what was once a token of affluence became a perfectly ordinary commodity. By the early 1990s, three out of five households had answering machines. Moreover, familiarity and comfort with the machines have transformed the way we use them. Most callers no longer feel that they are talking to a machine; they are addressing a person, with the machine a nearly transparent intermediary, much like the telephone itself. Terse, awkward recitations have given way to casual, chatty monologues.

At the same time, call screening has introduced an effective tool for avoiding communicating, such as when telemarketers, bill collectors, or relatives call. In addition, callers nowadays often prefer to leave a recorded message, making their communication without troubling with the niceties of a two-way conversation.

Today’s high-tech answering machines are about as small as they can get without making the controls inconveniently tiny. Low-cost microchips handle all the work and offer such new features as an individual voice-mail box for each member of a household. Tapeless models capture sound as binary data on a chip, compressed by mathematical algorithms and stored in memory to be reconstituted later as that long-dreaded call from your aunt in Minnesota.

The stand-alone answering machine may be an endangered species, its functions getting absorbed by centralized voice mail, the telephone itself, the fax machine, the computer, or some combination of them. Perhaps before long your computer will answer the phone and engage in a simple conversation with a caller. Then as our friends’ computers call our computers, we will silently listen in, observing what our machines have to say to each other.