Some 4 billion people own cell phones, every one of which gives off radiation. Recent studies show that those using cell phones for 10 years or longer have significantly higher risks for brain and salivary-gland tumors. Cell phone manufacturers and telecom companies are not required to label their products’ radiation output, so the nonprofit Environmental Working Group tested more than 1,000 phones. Below are the 10 best and worst phones available from major carriers. To see where your phone is ranked, go to www.ewg.org.