Despite what your grandmother might say, the jury is still out on a definitive link between cellphone usage and brain cancer. The World Health Organization has just completed the largest-ever study on the issue, drawing upon 10 years of research and 13,000 participants, but there isn't much to show for it. "The study doesn't reveal an increased risk, but we can't conclude that there is no risk," said its chief researcher. Making the results even more ambiguous, critics have highlighted the study's flawed methodology, saying that the WHO relied on participants to provide their own usage history based on memory rather than observation. Even worse, the study was funded in large part by the cellphone industry. An even bigger study along the same lines launched in the U.K. last month.