I have never been interrupted during a presentation by a ringing cell phone. However, I'd like to think if I was I would be creative enough to come up with a response like the video this week. The performer's look at the end of the video sums it up. Classic (pun intended).
WiX Working Group video of the week, violist plays along.
Related: Marc-André Hamelin's "Valse Irritation d'après Nokia" - http://www.youtube.com/watch?v=2QK3GS8_3rs