WAP Push messages are SMS messages that alert the user, and allow the user to open the URL sent. In most GSM networks, however, GPRS activation from the network is not generally supported, so WAP Push messages have to be delivered on top of the SMS bearer. On receiving a WAP Push, a WAP 1.2 or later enabled handset will automatically give the user the option to access the WAP content.
There are two types of WAP push message: Service Indication (SI) and Service Load (SL). SI messages are far more common than SL as they contain a text string.