Cellular (cell) phones first became widely available in the United States in the 1990s, but their use has increased dramatically since then. According to the Cellular Telecommunications & Internet Association, there were more than 320 million cell phone subscriptions in the United States as of June 2011, which is actually more than the entire US population. Along with the large and still growing number of cell phone users (both adults and children), the amount of time people spend on their phones has also risen sharply in recent decades.
Cell phones give off a form of energy known as radiofrequency (RF) waves, so some concerns have been raised about the safety of cell phone use. With respect to cancer, concern focuses on whether cell phones might increase the risk of brain tumors or other tumors in the head and neck area.