Nice. Thanks. Only question is are they bad for health? Don't want cancer.
Electromagnetic radiation is everywhere. Light is electromagnetic radiation. I just wanted to clarify that before the crazies start saying stuff like cellphones give you cancer.
The short answer is, they don't cause cancer. The long answer is below.
The frequency at which cellphones operate are between 700MHz and 2600MHz. These are in the radio waves range. At 2600MHz, the wavelength is about 0.115 meters (about 4.5 inches) long, at 700MHz, the wavelength is about 0.43 meters (about 16.77 inches) long.
Now you're going to wonder what does wavelength/frequency have to do with anything? For an electromagnetic wave to cause cell damage, the frequency has to be high enough such that the wavelength is small enough to ionize tissue (namely DNA). Ultraviolet rays, X-rays, and gamma rays are in this harmful range because their frequencies are extremely high/short wavelength.
How does the wavelength affect tissue? If the wavelength is approximately the same width of the base pair molecules in a strain of DNA, the wave can potentially hit the molecules and knock them out. This potentially causes mutation in the DNA, which can lead to cancer.
If the frequency is low and thus the wavelength is longer, it just passes through without causing harm. In fact, the signal on the 700MHz band is often better than the signal on the 2600MHz band because having a lower frequency/longer wavelength allows it to pass through buildings, etc. more easily compared to the 2600MHz band.
Every few years, a group of quack doctors will publish a report that says a certain % of the people in their study got cancer from cellphones. Then not long afterwards, another group of doctors will publish a report which refutes this.
I'll give you an example, back when I was in college, I read this cellphone study which said that 2-3% of the people in this town who participated in the study developed a form of ear cancer. These people also happened to own cellphones and used them regularly. Later, I found out that this same town has historically had this form of ear cancer in 2-3% of its population (with or without the cellphone variable).
I can make it look like a certain percentage of people in my town who has developed or will develop a certain cancer and correlate it with cellphone use if you give me enough time and resources.