Smartphones use radio waves for communicating with cellphone towers and access points. It is always better to have smartphones with less radiation for daily usage. Its a good approach to choose the smartphone based on the least radiation level. You will find the radiation levels of a smartphone in the regulatory information section of your smartphone operating system.
To find the details of the radiation level of your smartphone, you can type *#07# from the dialer. This will give you the details of the regulatory information.You may scroll down to see the SAR (Specific Absorption Rate) levels of your phone, this indicates the Radiation energy absorbed by your body while using the smartphone. The SAR values below 1.6W/kg are considered to be acceptable for usage.
If your smartphone is showing a value above the accepted level, then immediately get a new phone with lesser radiation levels.