I don't get this joke

Could someone please explainthis joke to me? Do you need to be able to read music? Thanks.

I think the notes in red are the Nokia ring tone.

But if you’re a brilliant musician, you do this.

Looks to me like it’s a takeoff on The Treachery of Images.

Yeah I think the joke is “turn off your fucking cell phone when you come to one of our performance!” (in that there is alternate music being played and it is the Nokia ring tone.)

Ah. OK, thanks all!