AT& T Inc., the large U. S. phone company and the one- time monopoly, left the payphone business at the beginning of 2009 because people were switching to wireless phones. U.S. consumers owning cellphones reached 80% by 2007 and 86% by 2012 according to the Pew Research Center. Consequently, the number of payphones fell from 2.6 million at the peak in 1998 to 1 million in 2006 (Crayton Harrison, “AT& T to Disconnect Pay-Phone Business After 129 Years,” Bloomberg.com, December 3, 2007). (Where will Clark Kent go to change into Superman now?) Use graphs to explain why a monopoly exits a market when its demand curve shifts to the left.