DTMF Shell "Live", with BASIC (tech demo)

A series of experiments demonstrating a "sound shell" over DTMF tones (like a "pure soft modem without hardware") is bound to culminate in an (admittedly very technical) "real world" demo, where one smartphone calls another and one computer controls another purely via DTMF tones. For the impatient — you can skip to the last minute "after credits", and there you shall see a BASIC interpreter computing and transmitting squares of numbers. (For anyone seeking to repeat this: for (much) better reliability, indeed do repeat each DTMF tone, as proposed in the video.)