[grantla]

If we are talking about phone numbers for humans - maybe true. Phone network routing numbers can and do contain A-E.

[zinekeller]

I mean, for the purposes of `libphonenumber`, PrioA-D is not used.

Also, as far as I know most things are sent out-of-band anyways, but I wouldn't be surprised if there's some legacy system out there which work only on DTMF.