Data on American text message usage

"Young adults are the most avid texters by a wide margin. Cell owners between the ages of 18 and 24 exchange an average of 109.5 messages on a normal day—that works out to more than 3,200 texts per month—and the typical or median cell owner in this age group sends or receives 50 messages per day (or 1500 messages per month).
Overall, the survey found that both text messaging and phone calling on cell phones have leveled off for the adult population as a whole. Text messaging users send or receive an average of 41.5 messages on a typical day, with the median user sending or receiving 10 texts daily – both figures are largely unchanged from what we reported in 2010. Similarly, cell owners make or receive an average of 12 calls on their cells per day, which is unchanged from 2010"
Source:  Data from Pew Internet and American Life Project 'Americans and Text Messaging', 19th September 2011
Full report from Pew here