When you Call into ext 107 does you single line phone ring? and have you tested the answering machine with the telco line plugged strait into it bypassing the sbx entirely?

If the SBX is functioning properly the SLT(single line Telephone) plugged into it should not be able to tell the difference between it and a normal TelCo line, which is why I ask if the answering machine functions the way you want it to when bypassing the SBX.