This number is from the American Lung [***]'n and as a charity, they are exempt from the Do Not Call list. It is probably dialed by a computer and then turned over to someone in a boiler room. If it doesn't get turned over to a worker quickly enough, it will appear there is no one there.
Been getting calls from this # for awhile. They are calling earlier and earlier. Just called at 8:15am, and call on Sundays too. So tired of it. Don't know how to get it to stop.