This is so much fun.
I keep my cell phone with me when I'm on stage and I either have someone call me while I'm in the middle of the presentation, or I just pretend the phone is vibrating and I have to answer the call.
Since the audience can't hear the person calling, you could fake the entire conversation if you wanted to.
Just recently I had the organizer call me on stage just as I was giving a small discount if the audience members wanted to buy my back-of-the-room package. The organizer was telling me that the discount I was giving was not good enough.
We started arguing about it on the phone which was making the audience members laugh.
Note: If you've listened to my 2 hour album on "Selling a Ton atthe Back-of-the-Room" http://www.kickstartcart.com/app/adtrack.asp?AdID=67431 you know that having the audience laughing in the middle of your close is a very good thing.
I gave in an dropped the price a little more on the package I was selling.
Immediately the phone rang again, with the organizer telling me that wasn't good enough. We had another argument and now the audience was really laughing.
I gave in again and dropped the price to the rock bottom and sold a ton.
You could pretend your mother or father is calling and nagging you about something. Or you could make up just about anyone that will allow you to make your part of the conversation funny to the audience.
Make good use of your cell phone while you are on stage and those will be some of the most valuable minutes you ever used.