PUSH was added to WAP 1.2, and is only available in WAP 1.2 environments. In short PUSH provides another way of sending data from a content or application server to a mobile user agent. The “traditional” way, PULLing is for the user agent to request the information, and then receive it. PUSH means that the server can send the data to the user agent without it having to ask for it.

The content or application server cannot send the data to the user agent directly, but will have to use a so called Push Proxy Gateway. This PPG sits between the internet based Push Initiator (the content or application server) and the mobile user agent. On the internet side, the Push Access Protocol is used, and on the mobile internet side, the Push Over-the-Air Protocol is used.

Note that the user agent does not automatically accept data from any content provider - only those that it has listed as trusted.

Both Openwave and Nokia provide tools to test WAP PUSH.

The full Push Access Protocol and Push-OTA Protocol specifications is available here.

Some devices might or might not support wappush, but might also have the ability to let the user click on a URL that was typed in a text message. Different devices and UI’s will also behave differently, of course. In some cases the user might be able to click on the URL directly from the message, just like in a web or WAP page, some devices such as Nokia will provide an extra item from the Options menu that says something like “Use address”.
Some examples and hints are provided by our friends at The Independent.

A good blog entry and discussion on the woes of WAP Push can be found at mobhappy