Mobile phones do not emit radiation... They use radiowaves, not microwaves or radioactive radiation... Your speakers react because the recieve radio signals from the phone if it's too close.
There was in fact a recent study that showed that mobile phones have no effect on the brain or any part of the human anatomy what so ever. There are studies made on rats and worms, but they are (obviously) not transferrable.
To cause any significant changes you'd need 10 mW/cm2 of radiation, and phones are nowhere near it.
Study from 97:
http://www.rfsafe.com/pages/articles/reuters_082697.htm
2002:
http://news.zdnet.co.uk/story/0,,t269-s2109832,00.html
Ice