Actually add an age property to each phone :) in step_04.ngdoc

docs/content/tutorial/step_04.ngdoc

@@ -70,11 +70,14 @@ var phonecatApp = angular.module('phonecatApp', []);
 phonecatApp.controller('PhoneListCtrl', function PhoneListCtrl($scope) {
   $scope.phones = [
     {'name': 'Nexus S',
-     'snippet': 'Fast just got faster with Nexus S.'},
+     'snippet': 'Fast just got faster with Nexus S.',
+     'age': 1},
     {'name': 'Motorola XOOM™ with Wi-Fi',
-     'snippet': 'The Next, Next Generation tablet.'},
+     'snippet': 'The Next, Next Generation tablet.',
+     'age': 2},
     {'name': 'MOTOROLA XOOM™',
-     'snippet': 'The Next, Next Generation tablet.'}
+     'snippet': 'The Next, Next Generation tablet.',
+     'age': 3}
   ];
 
   $scope.orderProp = 'age';