If you are in a car and using a cell phone, the cell phone locks on to different antennas as the car moves. As the car nears a cell phone antenna in the same cell phone network, less radiofrequency radiation is required by the cell phone to receive and send signals to the antenna. But as the car moves away, the cell phone uses more radiofrequency radiation to seek the closest antenna. 

Both RF and ELF are concerns with using a cell phone. There is a near-field and far field plume of radiation emitted when a cell phone is in use.  According to the book Radiation Rescue, the near field radiates about a foot from the antenna , with the most intense plume in a 7 inch diameter circle around the antenna. Wireless radiation penetrates approximately 2 inches into the adult brain. More radiation is absorbed in the brains of children talking on a cell phone placed to their ears.  The far field radiation passes through almost everything in its course to a receiver.

In addition, the switching battery pack on a cell phone creates very high levels of extremely low frequency electromagnetic fields (ELF).

Smart phones produce higher levels than cell phones of extremely low frequency emissions because they use more energy from the battery. Energy increases during the sending and receiving email, large files, and photos.  ELF on these phones have been recorded from 20 (milligauss) mG to 200 mG.