It's other cab drivers for the most part, sometimes friends and family. Driving around all day is extremely boring - as much as cell phone use sucks in general

It's other cab drivers for the most part, sometimes friends and family. Driving around all day is extremely boring - as much as cell phone use sucks in general while driving, they do what they do to stay sane. Besides the obvious boredom-killing, I've also heard of it being used as a safety feature. It wasn't that long ago that drivers would be robbed or assaulted (heck, an UberX driver here was just robbed a few weeks ago).