It's totally absurd.
Yup.
For one thing, it takes
twelve minutes for an egg to boil in a pot full of
boiling water. When you call someone else's cell phone, the two devices aren't sending a signal directly between the devices. They send the signal to the tower, so as far as placement goes, most likely one of the cell phones is having almost no effect on the egg, whatsoever.
Most cell phone antennas are omnidirectional. If we assume a perfect world, the radiation pattern would be a torus - looks like a donut - with the antenna going thru the donuts hole. The majority of the radation would be going elsewhere. Considering theres no real ground plane, they are kinda inefficient, also.
2 watt cell phone transmitter
Most cell phones today aren't even 2 watts. The old bag phones, maybe, but the newer digital ones? A conservative guess would put them at 50-200 mw. That was one of the big selling points, and why the batterys are so small/last so long. Put the towers everywhere, and you don't need a big signal to reach them.
Then theres frequency to take into account. The magnetron in a microwave is working at 10 Ghz +, and is focused fairly tightly into a radio-reflective cavity. Older microwaves used to go boom when you fired them up with no load inside - the mags self destructed with no place to sink their power. Your cell phone is probably down in the 2 Ghz range.
Even if you look at pure power INPUT - the microwave in my house dims the lights in the kitchen when it fires up the mag. My cell phone with its little 50mah battery pack couldn't even tickle the microwave.
Oh, yeah, been a licensed ham (N3KPR) since '90, and know a bit about radios.

So, basically, I agree with shmokes.