For some of you, Dial-Up modems may sound like a stone-age technology, but interestingly there are still some unique use-cases where these old devices may play a role for your IoT projects. In this article, I am going to touch some of such use-cases, but before we begin, let’s refresh some fundamentals.
What is a Dial-Up Modem?

“Modem” is an acronym for MOdulator/DEModulator. It converts the digital signal from your computer into an analog signal that can be carried by the phone line, and vice versa. For dial-up modems, due to the technology used to deliver normal phone service (POTS – Plain old telephone service), the fastest download speed available is 56 kilobits (one thousand bits) per second. As per V.34, the data upload speed is limited to 33.6 Kbps (maximum).

Before the days of mobile broadband, and before broadband itself even, there was a time where Internet access was provided by phone lines. To get onto a BBS or chat on ICQ required dialing a phone number and accoustically coupling a computer to the phone system. The digital data transmitted as audio didn’t have a lot of bandwidth by today’s standards but it was revolutionary for the time. [Nino] is taking us back to that era by using a serial modem at his house and a device that can communicate to it through any phone, including a public pay phone.

Alone in the Phone Booth: Acoustic Coupling in 2025
https://www.youtube.com/watch?v=1h9UcyUPYJs

Remember those “hacker movie computer connections” in the 1970s, 1980s and 1990s, as in “War Games”, “23″, “Sneakers”, “Hackers”, “Colossus” or “Tron”, even influencing the virus injection method by the Terminatrix in “Terminator 3″, and constituting the background of WHY Morpheus, Trinity & Neo needed specifically a payphone to escape the Matrix? Those types of connections that likely nobody had done for decades? On 30th July 2025, that counter was reset to zero: for I managed to establish a connection via modem & self made “acoustic coupler” to my Linux machine at home from my Macbook Air in a public phone booth — but not before dealing with broken phones, technically limited phones, phones clogged by dirt, prospective drug dealers, dancing youths and modem malfunctions. This is the story of this adventure — feast your eyes on the Midnight Commander, the Ed editor, ECL LISP & BWBASIC in this triumph of “modern technology”! #modem #acoustic #coupler

Dial-up over a linksys VOIP TA adapter – calling up nocharge one last time.

Monitor is a 9″ B&W “Miracle” VGA 640×480