Cell phones? Large amount of energy?
A cell phone probably puts out somewhere on the order of one watt of power, guessing by the battery life and the size of the battery. Of that, held near your head, 25% goes in the direction of your head -- the rest goes away. That leaves 250 mW. Of that, no more than 5% (and probably closer to 0.5%, or less) is absorbed by the tissues in your brain -- the remainder goes straight through.
That means no more than 12.5 mW of power, and probably much less than that, is actually absorbed by your brain. Your brain generates on the order of 25 Watts of power as heat; thus, the power output of a cell phone -- even using very generous estimates for the absorptivity of human tissue to the radio signal -- is about 2000 times less than the waste heat of the brain.
So there's no way a cell phone can damage brain tissue by energy deposit. The alternative -- that radio-frequency radiation has some special effect on brain tissue -- is more plausible. However, a single radio photon has nowhere near enough energy to be chemically active (compared to x-rays and gamma rays, which *do* ionize molecules and can thus damage cells and DNA). Will, then, the alternating electric and magnetic fields cause any sort of disruption? Not by any process I can think of. They're dwarfed by the natural electric fields present in neurons, for instance.
Another bit of compelling evidence is the level of RF power people have been exposed to with no damage. Amateur radio operators are frequently exposed to much higher power outputs, for instance, and there are reported instances of Navy personnel being zapped with high-intensity radar signals. In the case of the Navy sailors, the power deposit from the radar was indeed enough to burn skin, doing damage by the sheer amount of energy deposited. In this case, if there were any "special" damage mechanism in the brain, it would almost certainly show up. The fact that people have been exposed to such high levels of RF radiation without any obvious harm to the brain means that the miniscule amounts coming from cell phones and bluetooth headsets are almost certainly safe.
The real crux of the issue is that RF waves mostly just pass through tissue without doing much, so you need a whopping big amount of the things for the tissue to even be affected ... and in that case, you just get a general deposit of energy into the tissue: heat.
Of course, as pflanagan says, doubt is part of science ... but the above is the best analysis I can come up with (at this late hour).
BCloud: I would imagine it would depend on the rate (and efficiency) at which the particular drug is absorbed by the stomach. I have no clue about such things.
On DDT: It was never proven to cause harm (Rachel Carson's claims haven't been backed up). What it was proven to do was to stick around for a long time, something that's suspicious. To be on the safe side, just in case it caused environmental harm that we didn't know about, its use was discontinued. However, it's entirely plausible that a chemical -- moreover, a chemical that's supposed to harm one class of living things -- might harm other sorts of life, especially since biology is a chemical process that's not completely understood. It's more of a stretch to say that a low-level oscillation of electric and magnetic fields would have a mysterious harmful effect. The physics of radio waves is understood completely (Maxwell's equations); while we don't completely understand the biology with which they may or may not interact, we do know what sorts of processes that biology involves... and the two don't really seem to interact.