A word of clarification for those of you who may have seen my recent interview on a local television station: at one point I am shown stating, "... there is pretty overwhelming evidence that, if there is an effect, it is extremely small." My statement was meant to refer to the carcinogenic effect of powerlines, not cell phones. The research regarding cell phones and cancer is at a less mature stage, and I am not qualified to provide expert opinions on this issue.
I agreed to the interview, not to address medical issues, but rather to discuss how the cellular telephone system works, what kind of radiation cell phones produce, and how such radiation interacts with tissue (heating). The full interview from which the aired excerpts were taken concentrated on these issues.
If you are concerned about risks from cell phone transmissions, you may reduce your exposure to the electromagnetic radiation from cell phones considerably by increasing the distance between the antenna and your body. You may use an external microphone and speaker, or you may use an external antenna, perhaps mounted on the car roof. The ABS 20/20 report on cell phones and brain cancer referenced below indicated that holding the cell phone close to the face results in lower power at the brain than if the phone is held more vertically with the antenna closer to the head. Also be aware that the closer you are to a cellular tower, the lower the power output of your own cell phone, and the lower your exposure. Towers are much more closely spaced in areas of high population density, so you may expect less exposure in cities than in rural areas where towers are more sparsely placed.
You may find references below that address these issues.