Thanks for posting.
Precedence dialing is still done on the military phone networks, but using number combinations (Example: Entering 93 before a number is a priority call) rather than the separate tones and the Government Emergency Telecommunications Service has superseded Autovon for any civilian priority telco access.
Present-day uses of the A, B, C and D keys on telephone networks are few, and exclusive to network control. For example, the A key is used on some networks to cycle through different carriers at will (thereby listening in on calls). Their use is probably prohibited by most carriers. The A, B, C and D tones are used in radio phone patch and repeater operations to allow, among other uses, control of the repeater while connected to an active phone line.
The *, #, A, B, C and D keys are still widely used worldwide by Amateur radio operators for repeater control, remote-base operations and VOIP-based communications systems.
DTMF tones are also used by some cable television networks and radio networks to signal the local cable company/network station to insert a local advertisement or station identification. These tones were often heard during a station ID preceding a local ad insert. Previously, terrestrial television stations also used DTMF tones to shut off and turn on remote transmitters.
DTMF signaling tones can also be heard at the start or end of some VHS (Video Home System) cassette tapes. Information on the master version of the video tape is encoded in the DTMF tone. The encoded tone provides information to automatic duplication machines, such as format, duration and volume levels, in order to replicate the original video as closely as possible.