You can use HTML5 Websockets to introduce your own push messages. From Wikipedia:
"For the client side, WebSocket was to be implemented in Firefox 4,
Google Chrome 4, Opera 11, and Safari 5, as well as the mobile version
of Safari in iOS 4.2. Also the BlackBerry Browser in OS7 supports
WebSockets."
To do this, you need your own provider server to push the messages to the clients.
If you want to use APN (Apple Push Notification) or C2DM (Cloud to Device Message), you must have a native application which must be downloaded through the online store.
