Hi, I?m trying to make SIP driver (Telephony Service Provider - TSP) in Microsoft TAPI architecture for my university project. Currently I have frame of my TSP for managing Windows communication, built with some library and I want to use pjsip for SIP communication. Unfortunately I?m not the best programmer and now I don?t have much time for studies pjsip. I have found Simple PJSUA http://www.pjsip.org/pjsip/docs/html/page_pjsip_sample_simple_pjsuaua_c.htm And I wanted to use it in my TSP. In one of my TSP methods responsible for making call I put this sample with little changes. I put this sample into static method - init() of my new class pj_siptsp_call and in particularly place I?m using pj_siptsp_call::init(); to start pjsip code. Now I can make call thru this TSP but when I finish one and want to make another, this error occur: "Calling pjlib from unknown/external thread. You must register external threads with pj_thread_register() before calling any pjlib functions." I?ve read about this, when someone advised usage of pj_thread_register() but I don?t know exactly where and how I have to do this. My driver doesn?t have to be properly designed ? I just want to have ?make call? functionalities and that will be ok for my education ;-) I would be very thankful for any advices. Michael