We have 4 lines (connected to Patton SN4114) connected to the 3CX system plus one Skype gateway. I set an outbound rule for the skype (prefix "0"), but noticed that I haven't figured out how to let users "choose" what line to use when making a call. On our Grandstream phones, I set the line buttons to lines 1-4. What I see when testing them is that no matter what button I use to choose a line, it seems pretty random what line (phone number) it actually calls through. How can I set this?