Specific Absorption rate (SAR) is the amount of radio frequency energy absorbed by the body when using a phone. The value should be minimum for a good phone which cause no/minimum health problems. The Federal Communication Commission (FCC) standard for SAR limit of 1.6 watts per kilogram averaged over a volume of 1 gram of tissue for the head.
Make sure your Mobile phone SAR value is less than this limit. Though most of the high-end phones available in the market confers to this criteria, the low cost- models of almost all companies have high SAR values. Now steps are being taken by different governments to strictly enforce this limit to all mobile phones .
Any way, limit the time you spend talking and switch to other modes of data transfer like texting. Users in age limit below 20 years should take particular care not to use mobile phones for long. Devices like hands-free can also help you out from radiation effects.