This is a implementation of a REST wrapper using the REST APIs of Notification Hubs from a PHP back-end.
Initialize your Notification Hubs client (substitute the connection string and hub name as instructed in the Get started tutorial):
$hub = new NotificationHub("connection string", "hubname");
Then add the send code depending on your target mobile platform.
$factory = new NotificationFactory();
$notification = $factory->createNotification("apple", "Hello from PHP!");
$hub->sendNotification($notification);
$factory = new NotificationFactory();
$notification = $factory->createNotification("gcm", "Hello from PHP!");
$hub->sendNotification($notification);
This code is provided as-is with no guarantees.