When I call someone I want him to see my phone number. Now everyone only see my main number no matter which number I call from.
I belive I do this in Outbound Parameters but I cannot find out how:
Works for me. Must be either something in how your outbound provider is set up in 3CX or 3CX is sending the correct caller ID and your provider is ignoring the info and passing your main number as the only option. I would suggest you do a test call and study the event logs.
Before you contact your ITSP, you can check which number are you sending to them, install wireshark and see what number is going to them, just to be sure that from your side everything is ok...