Two weeks ago and last night one of our phones left a voicemail on another phone in the middle of the night around 3am. No one was working so there would not have been someone in the office to make the call. Both times the voicemail went to the same extension. The voicemails were a couple of minutes long and there's no sound on the voicemails. I don't know where to start on this one other than contacting my pbx vendor. Does anyone have some troubleshooting tips for me? Thank you.