World Health Organisation’s warning for mobile phone users:
A person using a mobile phone 30–40 cm away from their body – for example when text messaging, accessing the Internet, or using a “hands free” device – will therefore have a much lower exposure to radiofrequency fields than someone holding the handset against their head.
In addition to using "hands-free" devices, which keep mobile phones away from the head and body during phone calls, exposure is also reduced by limiting the number and length of calls. Using the phone in areas of good reception also decreases exposure as it allows the phone to transmit at reduced power.
Mobile phones are often prohibited in hospitals and on airplanes, as the radiofrequency signals may interfere with certain electro-medical devices and navigation systems.(also would frustrate and disruptive brain waves and the natural signals and communication among body cells )

Limitation of World Health Organisation’s  research:
WHO admit the limitation of scientific data on hand : the lack of data for mobile phone use over time periods longer than 15 years warrant further research of mobile phone use and brain cancer risk. In particular, with the recent popularity of mobile phone use among younger people, and therefore a potentially longer lifetime of exposure, WHO has promoted further research on this group. Several studies investigating potential health effects in children and adolescents are underway.

WHO admit that since the technology is too recent to rule out possible long-term effects. Mobile phone handsets and base stations present quite different exposure situations.

Limitation of BIOLOGICAL threshold:
WHO says that Biological effects are measurable responses of organisms or cells to a stimulus or to a change in the environment..However,the body might not possess  adequate compensation mechanisms to mitigate all environmental changes or stresses. Prolonged environmental exposure,even if minor,may constitute a health hazard if it results in stress.In humans,an adverse health effect results from a biological effect that causes detectable impairment in the health or wellbeing of exposed individuals. Complying with exposure limits recommended in national and international guidelines helps to control risks from exposures to EMFs that may be harmful to human health. The present debate is centred on whether long-term, low level exposure below the exposure limits can cause adverse health effects or influence people’s well being.

Serious warning from other EMF expert and scientists:
Do NOT give a young child (or even a pre teen), a cell phone under any circustances. Teach teenagers how to carry and use a cell phone with less exposure by using ear buds or the speaker phone, but never against the ear. Do not carry a cell phone in your pants or shirt pocket. Keep it at a distance from your body in a handbag, or briefcase, or on the car seat. Use your brains: keep the cell phone at least one-two inches away from you body (in a metal shielded pouch) if you must carry it.