Can one AngularJS controller call another?

There are multiple ways how to communicate between controllers.

The best one is probably sharing a service:

function FirstController(someDataService) 
{
  // use the data service, bind to template...
  // or call methods on someDataService to send a request to server
}

function SecondController(someDataService) 
{
  // has a reference to the same instance of the service
  // so if the service updates state for example, this controller knows about it
}

Another way is emitting an event on scope:

function FirstController($scope) 
{
  $scope.$on('someEvent', function(event, args) {});
  // another controller or even directive
}

function SecondController($scope) 
{
  $scope.$emit('someEvent', args);
}

In both cases, you can communicate with any directive as well.

See this fiddle: http://jsfiddle.net/simpulton/XqDxG/

Also watch the following video: Communicating Between Controllers

Html:

<div ng-controller="ControllerZero">
  <input ng-model="message" >
  <button ng-click="handleClick(message);">LOG</button>
</div>

<div ng-controller="ControllerOne">
  <input ng-model="message" >
</div>

<div ng-controller="ControllerTwo">
  <input ng-model="message" >
</div>

javascript:

var myModule = angular.module('myModule', []);
myModule.factory('mySharedService', function($rootScope) {
  var sharedService = {};

  sharedService.message = '';

  sharedService.prepForBroadcast = function(msg) {
    this.message = msg;
    this.broadcastItem();
  };

  sharedService.broadcastItem = function() {
    $rootScope.$broadcast('handleBroadcast');
  };

  return sharedService;
});

function ControllerZero($scope, sharedService) {
  $scope.handleClick = function(msg) {
    sharedService.prepForBroadcast(msg);
  };

  $scope.$on('handleBroadcast', function() {
    $scope.message = sharedService.message;
  });        
}

function ControllerOne($scope, sharedService) {
  $scope.$on('handleBroadcast', function() {
    $scope.message = 'ONE: ' + sharedService.message;
  });        
}

function ControllerTwo($scope, sharedService) {
  $scope.$on('handleBroadcast', function() {
    $scope.message = 'TWO: ' + sharedService.message;
  });
}

ControllerZero.$inject = ['$scope', 'mySharedService'];        

ControllerOne.$inject = ['$scope', 'mySharedService'];

ControllerTwo.$inject = ['$scope', 'mySharedService'];