Yesterday, I did more test, phone system would not release SIP trunks after called party hung up. it happened 1 out of 3 or 4 of the calls.
So I think it's not mobile twinning issue, it's actually the SIP trunks not release issue. As they are not released, system think call is still in progress, which makes mobile twinning not working.
So I upgraded firmware from 9.0.3.16 build 2 to 9.0.12.0 build 1006, issue remained when testing outgoing calls. first call to local was all right, SIP trunk was not released with 2nd call to my mobile, no voice with 3rd call.
then I deleted SIP trunks and rebuilt it, problem remains.
tested outgoing calls with analog phone, same issue.
Today we will go back to there and trace the calls with Wireshark, and try to get SIP provider involved.
