I have a user that claims her phone does not always ring, and calls end up going to voicemail because of this. The caller will then usually call back and ask why she didn't answer, as they heard it ringing on their end.
This has happened a couple times now, and the user swears up and down she isn't doing anything when it happens. Is there any way to tell if the phone is actually ringing all of the time? Traces or packet captures? Could this be an intermittently bad ringer?