How to display a pop-up alert on polycom 550?

I am using the 3.1 polycom firmware for 550 model.

On page 4-72 of the SIP 3.1 administrators guide there is a short note on how to get a pop up notice on the phones screen.

Any one tried this or know how to send a sip header from asterisk cli to the device to generate this pop up?

Using asterisk 1.4 on centos 5.2.

thanks.