An answer from Interphone is crucial for public health, Carpenter says. Although a handful of studies have been published on cellphones over the past few years, most have been statistically useless. For one thing, they surveyed too few people. Additionally, the majority of studies focused on the effects of cellphone use after several years, but in most cases brain cancer takes a decade to develop. Interphone looks at the influence of both short- and long-term use. That's not to say that the study is perfect. Interphone defines "regular" use as one call, once a week. It's possible that this definition underestimates the risk to people who use cellphones more frequently.