In article , TELECOM Digest Editor noted in response to Robert Bonomi:
[TELECOM Digest Editor's Note: As Robert knows, those four additional
> touch tone keys were known as A,B,C, and D. I forget the exact
> meaning of each, but my question is, did anyone with 'regular'
> service but with an Autovon phone ever try pressing those keys in
> a regular call? I did a couple times, and the immediate result was
> a 'fast busy' signal; the call would not complete. PAT]
On the PSTN, it somewhat depended on the switch and programming. 'Reorder' was the very-common switch reaction. There were a few switches that completely 'ignored' those signals.
[TELECOM Digest Editor's Note: But did you ever see/hear any that neither ignored nor offered re-order, but instead actually _did something_ ? I never did. PAT]