The iconic speaking clock is apparently making BT around £21 million a year, with the 74-year-old technology still proving remarkably resilient.
Although it has been hijacked by the likes of Lenny Henry (in the name of charity) and, controversially, Tinkerbell for a sponsored tie-in, there have been just four main speakers in its entire history.
And with 70 million calls a year, at a cost of 30p per call, that amounts to a staggering profit for an automated phone line.
"It's hard to say why the speaking clock is popular," a BT spokesperson told TechRadar.
"The speaking clock has been around for 74 years so a lot of people have grown up with dialling 123.
"BT's speaking clock is a national institution, viewed with great affection by the general public."
Today the talking clock is accurate to within five thousands of a second, a far cry from the original accuracy of one-tenth of a second and it still influences timings for Big Ben and the News at Ten.
You can read about the history of the speaking clock in a special TechRadar Feature
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