I don't think kids are sitting in a quiet playground next to each other texting.
You'd only text during class when you're not allowed to talk, or if the person you're texting is in another class, or if you're trying to find someone, or a whole heap of reasons which may not be related to normal conversation.
I don't buy it that texting is somehow wrong and that face to face communication is somehow some great social norm. Maybe I don't WANT to have others judge my body language, nuances in speech and more importantly, take some precious time out of my day to actually go see someone.
But most importantly, I find texting is supremely useful because the recipient might be busy and I don't want to disturb them, or a reply is not urgently required. Or, important information that must be documented (e.g. addresses or meetings).
Sexting is actually not really texting but sending MMS pictures. MMS can be optioned out of many different plans. I doubt kids are sending ASCII drawings of themselves.