Mobile data traffic is of wide interest, since so much hope resides in wireless broadband services. Unfortunately there is little solid information available.
Some interesting snippets can be found at the Opera Software Mobile Report Page, which presents a series of monthly reports on the Opera Mini browser for wireless devices. As an example, the June report states that in that month, 14.5 million users generated 46.7 TB of traffic, or slightly more than 3 MB per user per month.
A thorough study of mobile data usage in Finland by Antero Kivi was released in April 2008. It shows, for example, that 92% of the mobile data traffic came from computers, with browsing dominant, and P2P traffic very low. Traffic grew 11x between 2006 and 2007, but total volume came to only about 1 PB in 2007.
The Telecom Italia presentation deck from Nov. 2007, listed in the
Individual Service Provider Reports section gives some quantitative data about TI's mobile data traffic, which was about 1% of its backbone traffic.