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    T for touch-tone (because there’s also P for pulse, a whole other story)

    I’m old enough to remember when Touch-Tone (a trademark; {DTMF,tone}-dialing being the “more official” name) was a pay-for option. You could save some small amount of money every month by not having it. Hayes and ATDP saved me a whole like…$0.33 a month or something.

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      On the other end of the timeline, a few years ago I had a free rotary telephone and an effectively free VOIP line with an FXO port that only supported DTMF (and sadly no SIP or H.323 access; hooray for consumer-oriented service). I ended up wiring a 3.5mm TR jack into the phone and hooking that up to my computer, with a small shell script to play the appropriate DTMF tones from my computer. It probably saved me a whole $10 that year.

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        As a BBS operator, saving money by ditching touch tone was a critical money-saver. Those lines were never used to dial out. I think the feature cost more than a dollar a month.