According to a new Nielsen poll (as found on cnet), Americans now send more text messages than make phone calls. And 13-17 year olds send 1,742 text messages a month. Assuming an eight-hour sleep cycle, that means they're sending a text message about every 17 minutes of their waking days.
And, of course, someone has to read all those messages. I assume it's mostly other teens. Which means that for every message sent, one is read. Which then means that they are either sending or reading a message about every 9 minutes.
Passing messages back-and-forth more than 6 times an hour. Even if the reply is just, "LOL," that's a lot of readin' and writin'.