call iphone webservice api from an external system

I'm trying to built an app which listens to webservice calls. Is it possible to sent a request to an iphone?

O开发者_开发问答f course I can implement a service in the app which checks every minute if there is an event, but this would be very uneffective energy management.

Has anyone read something about such problemes and can give me a hint?

Greetings, matthew

That where push notifications are for.

Since it's not really possible to keep listening to a socket once your app enters the background. Only VOIP client are allowed to do this.