The National Cancer Institute has created a free text message service, called Smokefree T-X-T, that gives advice, encouragement and tips to help teens stop smoking. Teenagers who are interested in quitting sign up with the service and select a date to quit. They then receive regular text messages aimed at helping them stop, which continue for six weeks after their quit date, the time period which experts say is the most critical for cessation support. The Institute has also created a website where teens can chat about quitting. The program is part of the U.S. Department of Health and Human Services, and also includes a free smartphone app called QuitSTART, a guide with tips, a cravings tracker, and a monitor of attempts at quitting. Statistics show that 75 percent of teenagers own a cell phone, and 20 percent are smokers, leading experts to conclude that texting could be an effective means of helping this vulnerable group.