The missing step
An answering machine records a message on a device at your own telephone. Voicemail does the same job somewhere else. A call that nobody answers, or that finds the line busy, is diverted to a computer that plays a greeting and records the message in a mailbox that belongs to the called person. The diversion step, the transfer of an unanswered call to a message system, is what made voicemail possible as a shared service.
Why a new system was needed
By the 1970s businesses had answering services and desk telephones with message slips, but messages were slow to pass on and often garbled. Telephone tag, in which two people repeatedly miss each other, was a known cost. A system that could store messages for many people at once, and let each person retrieve their own, offered a gain in speed and reliability.
Two technologies were needed. The first was a way to store speech so that it could be recalled quickly. Magnetic tape was slow for many users, so engineers turned to digital storage of voice on the disks of electronic computers. The second was a way for the telephone system to send an unanswered call to the storage computer, and to tell it which mailbox to use. The programmable exchanges and private branch exchanges that appeared in the 1970s offered a path.
The first voicemail systems
Credit for early voicemail is often given to Gordon Matthews, an American engineer who in the late 1970s founded a company that built a system called VMX (Voice Message Exchange). It stored digitized speech on disks and allowed users to record, send, forward and delete messages from a telephone keypad. A patent was granted in the early 1980s. Other companies and laboratories worked on similar systems, and the claim of being first depends on what counts as voicemail.
AT&T introduced a system named Audix in the mid-1980s, and several other vendors followed. These were sold mainly to large organizations that could afford the equipment. A person in the office was given a mailbox number, a personal identification number, and a short list of key presses.
How the diversion works
When a call comes in for an extension, the exchange rings it for a set time. If nobody answers, or if the line is busy, the exchange diverts the call to the voicemail system, often using the same mechanism as call forwarding, and passes along the number that was originally dialed. The voicemail computer then knows which mailbox to use, plays the owner’s greeting, and records the message.
Some systems let callers press a key to escape, perhaps to reach an operator, or to hear a menu. The caller’s number, if known, can be stored with the message.
Telling the user a message is waiting
A voicemail system also needs to tell the owner about new messages. Early arrangements included a small lamp on the telephone, which the exchange or voicemail system switched on. On ordinary home lines, telephone companies introduced a stutter dial tone, a tone that broke into rapid pulses when the receiver was lifted, to signal a message. Later systems sent a visual indicator to telephones with displays, and eventually text messages or notifications.
From company system to public service
During the 1980s and 1990s, telephone companies began offering voicemail as a network service to ordinary customers. The service stored messages on equipment in the telephone company’s building, accessed with a code, and could be added to a home or business line for a monthly fee. It competed with the home answering machine but had advantages: it worked when the power was off at home, held messages when the line was busy, and could serve several people on a shared line with separate mailboxes.
Mobile networks included voicemail as a standard part of service, since a phone that is switched off or out of range cannot answer. Calls to an unreachable phone are diverted to the mailbox automatically.
Visual voicemail and transcription
Answering machines had used magnetic tape, which is one reason voicemail seemed so different when it arrived. In 2007, smartphones introduced visual voicemail, in which messages appear in a list that can be played in any order, much like email. Some systems add automatic transcription, though accuracy depends on the speaker and the quality of the line. Text messages and voice notes in messaging apps have reduced the use of traditional voicemail for many people, and some users now ignore their mailboxes. Many businesses now rent mailboxes from cloud computing providers. Even so, voicemail continues to serve businesses, services and people who prefer the telephone.
Why it mattered
The diversion of an unanswered call to a mailbox helped set a norm: you can leave a message and expect it to be heard later. The transfer from the call to storage was a step toward a world in which most communication is not simultaneous. In that sense, voicemail connects the ringing telephone with the email inbox.