U.S. teenagers are sending or receiving an average of 3,339 text messages a month, more than six every hour they’re awake, according to a study released Thursday by Nielsen. Teen girls aged 13 to 17 were the most-active users, receiving 4,050 texts per month. Teen boys outpaced other male age groups, receiving an average of 2,539 texts per month. Young adults came in a distant second with 1,630 text messages per month. The company compiled its study using recent data from the monthly cellphone bills of more than 60,000 mobile subscribers, as well as survey data from more than 3,000 teens.