I would like to use XMPP so that my application will send out updates to an android phone (1.5 and higher). I pretty much want to use XMPP to send push notifications to the phon
That would depend on the nature of your push (is it a point to point or pub sub). In either case, you will need an XMPP server that your clients and application are connected to. This will be the means for your application to send notifications to the clients.
Not sure what you mean by "I need to use my webapplication to what google implements". Your webapplication would be a client to the xmpp server, just like your phones. You cannot use xmpp to simply talk to your webapplication, unless it happens to be a bosh enabled xmpp server itself, which I would guess is not likely.
You can use Smack for your client communications, and any one of the many available servers.
If the communication is directed at specific clients, then creating a chat between the application and client is probably the simplest means. If it is more of a broadcast, then you could use either MUC (multi user chat) or pubsub.
Generally, you would implement this as a pub-sub feature. Pub-sub is basically the publish/ subscribe paradigm: you publish something and they receive it.
Assuming you have an XMPP server setup that supports the pub-sub protocol extension (like eJabber), in your app, you would login to that server and subscribe to a node (where your update notifications would be sent), and with your subscription you would have to add a handler to handle any notification on that node.
On the server side, when you have something that all of your clients need to know about, you would publish the update to the same node that the clients subscribe to.
For more info, see http://xmpp.org/extensions/xep-0060.html