The popular esp8266 wifi microcontroller was initially sold as a wifi interface to other microcontrollers, communicating over a serial interface, using AT commands. Indeed this was the first esp8266 I came across (ESP-01) - a cheap wifi interface for an arduino. Later folks discovered that the esp is more powerful itself than an arduino, but I think the stock firmware that comes on the chip is the serial-wifi interface using AT commands.

Yes, I was wondering if I read that right, but it seems that AT commands are still in use.

Us BBS nerds used to know AT commands by heart. We would send instructions to our 2400 baud Hayes modems using QModem:

   ATZ = reset

   ATDT1234 = dial 1234 on a touch tone phone (DP for pulse dial)

Those of us who later moved to US Robotics modems started learning proprietary USR ampersand codes.

   ATH0.

Dialup was still a thing in this century, even if it feels like a long, long time ago. You could still reset people's connections by having them echo ATH0 back to you, if they were on a bad setup.

As recently as 2001 the majority of americans used dialup to connect to the internet. AOL was the worlds biggest ISP, and carried more than 50% of all US web traffic.

Anything talking to a modem is using them still...

From what I understand, this is because GSM is based around the model of a voice/data modem.

The phone OS itself would actually use something like the QMI (Qualcomm management interface) protocol or MBIM for modem cards.

The Hayes/AT commands are still used either for debug purposes, or for non-smartphone use cases like IoT.

They're used by a variety of communication devices. I recently worked with some Phoenix Contact industrial bluetooth devices that used Hayes commands for configuration.

Of course.