Chances are, if you reached out with your arm right now, you could get your smartphone (if you're not reading this on your phone already). Mobile telephony is different - rather than a medium, it has become a layer over our lives. We use it while watching TV, driving (we text in a moving car with lethal consequences - such as a spelling error) and even operating heavy machinery. You could say it's something like the radio, but when you need to phone to chirp in on the radio, it's a lot more difficult than a retweet