Did the Bell System ever use the fourth DTMF column (1633 Hz, for A, B, C, and D, or FO, F, I, and P) for anything other than Autovon?

[brouhaha@mastodon.social]

Did the Bell System ever use the fourth DTMF column (1633 Hz, for A, B, C, and D, or FO, F, I, and P) for anything other than Autovon?

[atax1a@infosec.exchange]

@brouhaha we heard some places would hide test numbers under there, but never confirmed as such

[brouhaha@mastodon.social]

@atax1a
Interesting.If they did that back in the olden days, they'd only be able to dial such a number from the same exchange, because MF signaling could only outpulse zero to nine. Maybe SS7 can send those.
For the same reason, an Autovon phone number couldn't contain FO, F, I, or P.
And of course, the same goes for * and # (the latter being A in Autovon).

[atax1a@infosec.exchange]

@brouhaha yeah, as we understood it, it would be for local test numbers only. the trunk test numbers would use an otherwise illegal 101 code so that they could be outpulsed to from other trunks