I found this thread from earlier this year which is closed without a solution: https://www.3cx.com/community/threads/tls-on-a-sip-trunk.43517/ I have only started testing 3CX by installing it onto a cloud VPS, checking the compatible trunk providers for Germany and chosing EasyBell from your list: https://www.3cx.com/community/threads/tls-on-a-sip-trunk.43517/ Btw. in that list, easybell is linked to this URL: https://www.3cx.de/docs/deutsche-telekom-sip-trunk/ which doesn't make sense as that link is about a different provider. So I checked EasyBell and they market themselves with the following features: - hosted in Germany - TLS ZRTP SRTP encryption - compatible with 3CX Now after connecting my easybell trunk to 3CX, I see I can enable SRTP for the trunk but I don't seem to have any control over how I am connecting to the trunk: UDP/TCP/TLS or am I simply missing where to set this up? Since my PBX is in the cloud, I need to make sure all connections to it are secured. So far this is done by only using 3CX clients via the 3CX tunnel and I might setup TLS SIP between my end users devices and the PBX but what about the route between 3CX and the trunk provider?