Recording while playing a background music?

I guess it’s a question has been answered 1k times. but could anybody give me a hint on how to record sounds while playing a background sound track to him. I’m trying to do a telephone karaoke system.

I dont see any problem…

Answer
Monitor
Playback

Correct me, if I’m wrong

p.s. have no place to try at this time, but we have installations, where
Monitor
Queue
are recoding callers while playing Queue’s background music

I did not know the Monitor command can do the trick.
thanks for the hint!