I'm with DJS & the others. I mean, I'm all for prank calls, any day.
But, you've got AMIII on the phone and you make it a joke? Why not call him out on his BS? Say how offended you were and that you were following Matthew 18 to tell him you were offended by his bigoted, Pharisaical attitude, and ask what defense he has for that behavior. Let him hang himself even more with his own rope.
If he hangs up on you, then he looks like a big @**hole. If he gets all self-righteous and indignant, he looks like a big @**hole. If he humbles himself, admits it was harsh, then you have a recording of him admitting such!
Win-win-win, in that case.
Pranking him, although probably fun and entertaining for exJWs, only accomplishes two things: to those that are still in that happen across it, it "confirms" that apostates are evil and mischievous; and to AMIII, it justifies his actions because Satan is persecuting him so he must be right.