I live near the Coast Highway and must see well over 100 cyclists per day. Seeing a rider talking on a cell phone is common. Personally, I leave mine on vibrate and in my bag while biking.
I was watching the run portion of a triathlon several years ago and saw a guy run by while talking on his phone. I told someone that my day would be complete when I see a runner smoking. Sure enough, here comes a guy with a cigarette.