The Cisco SPA 500 Series IP Phones support the SIP NOTIFY XML-Service event as a means to trigger XML services via SIP NOTIFY messages. On receipt of a SIP NOTIFY message with an XML-Service event, the IP phone challenges the SIP NOTIFY with a 401 Unauthorized response if the message does not contain correct credentials. The client must be furnished the correct credentials using MD5 digest with the SIP account password for the corresponding line of the IP phone.
The body of the message may contain the XML Service URL, which will be triggered at reception of the SIP NOTIFY message.
Note: We removed the direct support of XML syntax on the SIP NOTIFY message, based on security concern. Starting with 7.4.4, SPA500 phones will be able only to get a XML service URL (as highlighted in the example above), which will be "launched" to obtain the XML code.