Edit in JSFiddle

demo = angular.module('demo', [], '');

demo.controller('DemoCtrl',

function ($scope, DemoService) {

    $scope.$on('asyncResult', function (event, data) {
        $scope.foo = data;
    });

    $scope.makeAsyncCall = function() {        
        DemoService.makeAsyncCall($scope);
    };

});


demo.factory('DemoService', function ($http, $rootScope) {
    var service = {
        makeAsyncCall: function (theScope) {
            console.log('making a call...');
            $http.get('/echo/json/?a=b&c=d').
            success(function (data, status, headers, config) {
                theScope.$broadcast('asyncResult', 'it worked!');
            }).error(function (data, status, headers, config) {
                theScope.$broadcast('asyncResult', 'it failed');
            });
            console.log('done');
        }
    };
    return service;
});

<div ng-app='demo' ng-controller='DemoCtrl'>
    <input type="button" ng-click="makeAsyncCall()" value="DoJSON" /><br/>
    Result : {{foo}}</div>