code: function(topicArn, endpointArn) {
          var params = {
              TopicArn: topicArn,
              Protocol: 'application',
              Endpoint: endpointArn 
          };
  
          return this.svc.subscribe(params);
      }
docs: shorthand for device specific registrations, assumes the endpoint is an arn, and presets the protocol
  to 'application', which is used for mobile devices