Robert B>> Autovon used "standard" Touch-tone phones. Ones with *all* the
>> buttons, including the 4th column of 4.
> It wasn't that way at my father's installation, an army arsenal
> and research center.
> [BTW, a "standard" Touch-Tone phones does not have the fourth column.
> Further, plenty of Touch Tone phones introduced in the early years had
> only 10 buttons, not 12. We had such a set at home.]
It was very easy to modify the 12 button phones to use all 16 tones. You just used a push button toggle to swap the 3rd column to
4th column mode.And even those 10 button phones could be made to emit all 16 tones because both the 10 and 12 button pads share the same rows/columns of frequencies.