Cell phones have burst onto the scene, threatening to take over our lives. They also pose troubling health issues. Most of the nation's 111 million cell phone subscribers use phones in their cars. At least nine local jurisdictions bar handheld phones while driving, and dozens of states are considering bans. But the industry says cell phones are no more dangerous than car radios and that the increased productivity and usefulness in emergencies outweigh the safety costs. There is also persistent concern over whether prolonged cell phone use causes cancer, genetic damage and other serious health problems. Recent studies found cell phone users had no higher risk of brain cancer than non-users, but some scientists suggest it could take 20 years or more for those cancers to be detected.