Cell phones cannot cause cancer, because they do not emit enough energy to break the molecular bonds inside cells. Some forms of electromagnetic radiation, such as x-rays, gamma rays and ultraviolet (UV) radiation, are energetic enough to break the bonds in key molecules such as DNA and thereby generate mutations that lead to cancer. Electromagnetic radiation in the form of infrared light, microwaves, television and radio signals, and AC power is too weak to break those bonds, so we don’t worry about radios, televisions, microwave ovens and power outlets causing cancer.
Where do cell phones fall on this spectrum? According to physicist Bernard Leikind in a technical article in Skeptic magazine (Vol. 15, No. 4), known carcinogens such as x-rays, gamma rays and UV rays have energies greater than 480 kilojoules per mole (kJ/mole), which is enough to break chemical bonds. Green-light photons hold 240 kJ/mole of energy, which is enough to bend (but not break) the rhodopsin molecules in our retinas that trigger our photosensitive rod cells to fire. A cell phone generates radiation of less than 0.001 kJ/mole. That is 480,000 times weaker than UV rays and 240,000 times weaker than green light!
Even making the cell phone radiation more intense just means that there are more photons of that energy, not stronger photons. Cell phone photons cannot add up to become UV photons or have their effect any more than microwave or radio-wave photons can. In fact, if the bonds holding the key molecules of life together could be broken at the energy levels of cell phones, there would be no life at all because the various natural sources of energy from the environment would prevent such bonds from ever forming in the first place.