Microwave ovens use a frequency of around 2.45 GHz, not 800 MHz like
cellphones, however close to the 2.5 GHz cordless phones. It's not necessarily
the frequency that one should be concerned about, but rather the relative RF
power density levels produced by each device and its proximity to biological
systems. Because cell phones/cordless phones emit such a small
power density levels, there is no observable biological effect, i.e. heating
tissue. Microwave ovens on the other hand are purposefully designed to heat
media in via HUGH amounts of RF deposition in the oven chamber via more than
1000 watts. It takes hugh amounts of RF to heat tissue because the effect is
so inefficient being we are mostly water. Long chain molecues are more
efficient at absorbing RF, but again it takes very large amounts of RF to
produce any heating effect from friction caused by vibrating the long chain
molecules together.

The distinction between a cordless phone/cellular phone and a microwave
oven cannot be more clear. It like a match stick burning at a distance of
several feet and a roaring fireplace fire at the same distance...one will not
have any effect on you, the other will certainly warm your skin. Its as simple
as that.

Bruce.