power ups??
The GSMy type blokes who I speak with say that one or two phones aren't a problem. But as you get further and further away from a base station, like you would when you are taking off, the handsets crank up their signal strength to try to stay connected. (Which is why your battery goes flat quicker in poor signal areas)
So if on a flight full of business people, each with a phone and a crackberry, you could have up to 1500 devices attempting to get signal, all ramping up to nearly a watt of power, doesn't sound much, but my microwave is only 800 watts and it nuked the crap out of my curry last night!