I used a pager and then a cell phones for many years and always carried on my left pocket. Then, as dcsos mentions, I'd feel a buzzing sensation like my blood was going thru a small area at regular intervals. I checked with my doctor and it was indeed a Phantom Vibrate, After checking further I found where you should alternate sides occasionally if you clip it to your pants pocket for instance,

May not bother everyone but it is a real thing, courtesy of modern technology. LOL