First, studies have not yet been able to follow people for very long periods of time. When tumors form after a known cancer-causing exposure, it often takes decades for them to develop. Because cell phones have been in widespread use for only about 20 years in most countries, it is not possible to rule out future health effects that have not yet appeared.
Some studies have found a possible link. For example, several studies published by the same research group in Sweden have reported an increased risk of tumors on the side of the head where the cell phone was held, particularly with 10 or more years of use. It is hard to know what to make of these findings because most studies by other researchers have not had the same results, and there is no overall increase in brain tumors in Sweden during the years that correspond to these reports.

Another way to think about the situation is to consider the steady state power emission of .02 Watts and ask how long it would take to heat up your body by one degree Celsius if your entire volume was exposed. Take your body mass to be 100 kg and approximate it as being composed entirely of entirely of water. If all of the radiation was absorbed and went into heating you up (which it isn’t), it would take 20900000 seconds (specific heat*mass*1 degree/power) or 241 days to heat you up by one degree. Fortunately, you have metabolic processes in your body, or possibly air conditioning, to mitigate this heating.
Among the hundreds of smartphone cases available for iPhone and a bevy of popular Android phones, there are some that claim to reduce the amount of radiation your body absorbs when you have the handset close to your body. Pong Research is a US brand that offers a range of products fitting this description, as is Cellsafe, a company based in Victoria, Australia.
Radiation is all around us. Power lines, appliances, and electronic devices all emit electromagnetic frequencies. One source that many of us keep close, perhaps too close, are cell phones, tablets, and other mobile devices. They all use radio frequency (RF) electromagnetic energy, a form of non-ionizing radiation, to communicate. Research has shown that this type of radiation is not benign or harmless to the human body, especially children. Exposure to cell phone and Wifi radiation has been linked to fatigue, dizziness, mental fog, and even worse. As a result, the demand for products that reduce exposure to device radiation is on the rise. In fact, "How can I protect myself from cell phone radiation? What do you recommend?" is a question we get all the time. So, to help, I wanted to offer my thoughts on five products I've found that I believe are worth a look if you're interested in reducing your exposure to cell phone and mobile device radiation.
Consumers should utilize an air tube headset as a safer alternative to wired headsets or in-ear Bluetooth headsets, use the speaker feature and keep phones away from your body unless there is RF radiation shielding between the wireless device and cell phone users body.  When carrying a phone on your body it’s highly recommended to use either an RF Safe flip cover radiation shielded phone case or pocket shield to deflect excessive radiation away.
“I think the overall evidence that wireless radiation might cause adverse health effects is now strong enough that it’s almost unjustifiable for government agencies and scientists not to be alerting the public to the potential hazards,” says David O. Carpenter, M.D., director of the Institute for Health and the Environment at the University at Albany in New York and one of the authors of the recent letter to the U.N. and WHO.
The CERENAT study, another case–control study conducted in multiple areas in France from 2004 to 2006 using data collected in face-to-face interviews using standardized questionnaires (18). This study found no association for either gliomas or meningiomas when comparing regular cell phone users with non-users. However, the heaviest users had significantly increased risks of both gliomas and meningiomas.

The government’s policies must change. Cell phone users should make their voices heard to prompt the FCC and manufacturers of cell phones and cases to ensure that these accessories never increase and, to the extent possible, decrease, users’ radiation exposure. At minimum, the FCC must take cell phone cases into consideration when it updates its standards to ensure that the use of a case will not expose people to more radiation than its legal SAR limit.  
According to Dr. Devra Davis, who wrote Disconnect: The Truth About Cell Phone Radiation, cell phones are dangerous because they emit erratic signals capable of disrupting resonance and DNA repair. As long as your cellular phone is on, it sends out radiation intermittently. Even if you don’t take your phone out of your pocket all day, it continues to expose you to radiation. Dr. Joseph Mercola, founder of recently wrote an excellent article on the dangers of cell phones and provided common sense ways we can protect ourselves and our family from the electromagnetic radiation it emits.
But the pair of studies by the US National Toxicology Program found “clear evidence” that exposure to radiation caused heart tumors in male rats, and found “some evidence” that it caused tumors in the brains of male rats. (Both are positive results; the NTP uses the labels “clear evidence,” “some evidence,” “equivocal evidence” and “no evidence” when making conclusions.)
In addition, the findings might be influenced by the fact that the study subjects owned cell phones that were in some cases manufactured two decades ago. The way we use cell phones and the networks they’re operated on have also changed since then. Last, cancer can develop slowly over decades, yet the studies have analyzed data over only about a five- to 20-year span.
What the study showed: Self-reported cell phone use was not associated with an increased risk of glioma, meningioma, or non-central nervous system tumors. Although the original published findings reported an association with an increased risk of acoustic neuroma (14), this association disappeared after additional years of follow-up of the cohort (15).