[Freeswitch-users] Is possible from dialplan to detect if called party is online?

There some condition that let to check if the called party is currently registered and online, before giving the called a return code? We need to manage a condition where the called number is an iPhone and is usually "always offline" and we need to wakeup the voip client with a "push notifcation". But before doing the push notification we should check if the user is already registered/online or not. Don't know which path to follow Fabio