My entire dev team (all 4 of us) have started doing burpees at 11:00am and 3:00pm everyday. Great all-around excercise that gets your heart racing and even works out the whole body. Japan has a milder version, called Rajio Taiso.

Not sure if I'd be able to walk while in a meeting, even if its at a slow pace. When I'm working out, I usually try to get into "the zone" and I'd probably have difficulties staying focused.