To my knowledge, None.
In 2000, the Independent Expert Group on Mobile Phones chaired by Sir William Stewart undertook a comprehensive review of the scientific literature. It concluded that the “balance of evidence to date suggests that exposure to radiofrequency radiation below international guidelines does not cause adverse health effects to the general population” (www.iegmp.org.uk). A more recent report by the Health Protection Agency in 2004 on Mobile Phones and Health came to the same conclusion. This advice is available on the website of the Health Protection Agency
(www.hpa.org.uk/radiation).