You can do it by embedding a call-in-by-cell-phone poll within a PowerPoint presentation. The service by Poll Everywhere (http://www.polleverywhere.com/) is free, with limited use. Here’s how it works: Type the question for the audience, followed by a few possible answers. The poll can be downloaded as a presentation slide. Audience members send their answers by text message (they might type in “CAST 0001” and send it to 41411), and the results are updated on-screen.