TAP? The additional button on a DTMF telephone

[HowardPgh]

What does the TAP button do on this mid 80s phone?

[Key2871]

Tap is another word for flash, a quick break in the off hook condition. Takes you to another mode with lines so equipped. Such as call waiting, etc.

[Babybearjs]

why in the world would they change that? they just should have relabeled it "Recall"

[RB]

We used that function to switch from an active call, to accept a new call coming in.
effectively placing the first call on hold.
a second tap, would switch the two calls back to the first call, and place the second call on hold.
and if it worked right, you would not hang up on one of the callers.