Twenty years ago computers and telephones were very big and bulky. Computers were placed on the floor and didn't really move while phone were placed in a stationary base connected by cords and wires. They both emitted Electromagnetic Fields (EMFs), but were relatively safe, because they were used a safe distance away from the body.
Today, the computer and phone have merged into one device that fits in the palm of your hand. A smartphone is essentially a small computer, yet has many times the computing power of traditional computers. There are no cords to connect you to a base. When turned on in your pocket or being used against your head, the cell phone touches some of the most sensitive parts of the body. Although the cell phone produces lower levels of radiation then past computers, they are now used much closer to the body and for longer periods of time, thus creating more health risks than in the past.