By the way, if you call the number back,m they'll ask you for your zip code. then they will let you select 'i plan to pay in the next 7 days.' so if you do get this message, it doesn't mean your phone is about to be immediately shut off, but it's best to pick up when it calls or call back!
definitely not a scam or telemarketer, calling back could keep you from getting your phone cut off!