I was under the impression that low frequency waves (all the studies being on frequencies lower than those used by cell phones, so I still haven't been concerned, but maybe I should be) showed that they could vibrate DNA and chance how it is folded, adjusting its epigenetic profile. Why do you assume that the only way to cause cancer is "molecular damage"?
Biomolecules are remarkably fast (picosecond timescales) at dissipating excess heat into the solvent, like heat from an excited vibrational mode. In order to cause serious damage through unfolding, I think, you would need much higher intensities than a few milliwatts from a cellphone. Serious local heating requires visible, UV light and above. Sunlight, however, does massive damage to all parts of your skin, including base pair changes in your DNA beyond epigenetics but your body has repair mechanisms, which recover changes and/or destroy damaged cells. Proof of cellphone induced damage would be remarkable.
However, given the huge amounts of exo planets discovered everywhere around us in the last year or two, I consider it highly unlikely that we are alone.