I want to know whether we can implement our own SIP stack on non jsr-180 phones. I have heard that as along as communication through UDP/TCP is possilble on handset, we can implement our own SIP stack. Or can we instead port the existing Java JAIN SIP API on J2ME or can we import the classes of jsr-180 into non jsr-180 phones by putting jsr-180.jar into lib folder? What technical difficulties would come while doing so? I will welcome any suggestions on this....