There isn't an official one built in to the framework at the moment but there are several groups that provide push based notification systems for webOS. mremond has been on the forums showing his OpenPush system (http://www.openpush.im) or you could use something like webosworld's Villo services (http://webosworld.com/villo-services/) which is built on PubNub for push notifications (http://www.pubnub.com/). I'm sure there's even more you could choose from.
