President Barack Obama is seen here talking on his mobile phone - somewhat of an unusual photo nowadays. For the vast majority of us, when we talk on the phone, our social filters largely, or at least partially, drop away. Ironically, we express ourselves very openly nonverbally while on the phone, but of course the person we're speaking with cannot see us - of course, those around us can see our behavior. However, if this same person were standing next to us in an identical conversation, our body language would usually be dialed-down. The same nonverbal communication and emotions are still expressed, but they're simply diluted and harder to see. Thus when politicians, business associates, clients, politicians, friends, family members, etc. are talking on their cell, it's a fantastic opportunity to nuance their body language baseline behavior. We also usually have a fair amount of "background information" regarding the subject matter being discussed, and as we correlate their verbal with their nonverbal - which is always a goal of good body language analysis - we will be able to use this to our dramatic advantage when this same person on another occasion is speaking to us - for they have given us glimpse inside their "primer".
Observing another on a phone call is a body language cheat sheet into their psyche. Read well.