I have attempted to look through the documentation for the M300, but I cannot seem to locate any options that would control ring volume based on what kind of call the M300 endpoint is receiving. We have a PBX system with internal extension numbers, when calling the M300 user from other endpoints within the PBX the call rings properly. External calls ring extremely quiet as opposed to the internal calls. Unfortunately I am unable to get my hands on a physical unit at this time, as the user for this phone isn't close by. Is there any insight you can provide into my issue?