[telegraph]

"Since texting is usually a binary activity (the texter sends a text for every text they receive) we can guess that Echo writes about 7,000 text messages per month"

A huge oversimplification and probably inaccurate. Especially since most phones made in the past few years have the capability to send a text to multiple recipients, I highly doubt that Echo is typing as many texts as she receives -- both because she's more likely to get mass texts, and because she may herself be sending mass texts (which are charged as multiple texts, but are only typed once). I haven't been a teenager recently, but I also suspect that there is a lot more one sided texting than you'd expect (especially directed at pretty, popular girls).