Issue regarding SIP testing

Is there any way to perform load testing for SIP protocol using loadrunner?
Scenario is: I am having 500 SIP phones who is calling to 500 other SIP phone over internet. There is an application server which handles all the load. Once the session has been established, media will be send and at the end session will be terminated. Is there any way through loadrunner that I can do this?
Another issue is if one SIP phone is calling to other than there must be an answer by the called SIP phone,so how could called SIP phone know that some call is for him?
Please specify, if more info is required?