Pooled studies from several countries show no increased risk of acoustic neuroma: This form of tumor was seen as most likely to be the result of exposure to an adjacent cellular phone. The British Journal of Cancer has published the study review which shows no substantial risk--meaning no statistically significant correlative factors--in cell phone use in the first decade of use.
Given that phones produce less and less signal strength as they've moved to more sophisticated digital technology, this should reduce any remaining potential harm over a longer term. Study authors and cancer charities in England recommend continuing to follow the issue to examine whether risks exist over periods longer than a decade of use.
Given that cell phones use substantially more power than Wi-Fi and are concentrating their signals much closer to the brain, this is another good piece of positive information in reducing concern that Wi-Fi and similar technologies have any effect on human health.