Android Push Notification with Google Cloud Messaging including PHP Server Code
http://thanksandroid.com/android-push-notifications-with-google-cloud-messaging-part-1/ http://thanksandroid.com/android-push-notifications-with-google-cloud-messaging-part-2/
In the GCMDemo project, set your project number or sender key in Constants.java In PHP Server code, set your server API key in GCM.php
The demo app sends GCM registration id and message to server and receives it as GCM message from server.
In your app, you may want to save GCM registartion id in the database on your server and send message from server whenever required.