The WHO just finished a large 10-year study:
A report by the World Health Organization shows that long-time cell phone users are at serious risk of brain tumors. The entire report will be published and released by the end of the year.
The WHO is apparently a well-respected organization, so I’m finding it hard to be skeptical so far. I’m not really concerned about this myself, as my cell phone use tends to be in the range of minutes per week, but I realize I’m not the average cell phone user.