> a DTMF tone. (Is that a redundant acronym phrase?) Technically not, since "DTMF" is a proper noun referring to the overall encoding system, and is used as a

> a DTMF tone. (Is that a redundant acronym phrase?) Technically not, since "DTMF" is a proper noun referring to the overall encoding system, and is used as a adjective indicating that this particular tone is associated with that system. Compare "That farm raises KFC chickens. (That is, chickens intended for use by the resturant (chain) that calls itself "Kentucky Fried Chicken".)". Or "The left is what a MacOS window looks like, and the right is what a Windows window looks like.".