Equipment: Trixbox (latest stable) on a Linux server.
Aastra 9133i IP Phone

I have a calling group with 12 extentions fielding calls from 8 lines in a trunk. When a call comes in, every extention rings at the same time. The "winner" is the person who picks up the phone to answer the call. Two things happen with this installation:

1) A person will pick up the phone, hear a dialtone, dial their number, and suddenly be speaking with someone making an outside call coming in.

This phenomena happened to me as I called into the clinic--I heard a pause, some dialing sounds, then a person inside the clinic confused as they thought they were talking to the person they called, not me.

In short, the phone does not appear to respect the dialtone--it will simply route in a call even if the phone is off the hook.

2) A person checks the common voicemail. It's reported that the voicemail will be fine for awhile but then get into a weird "prompt loop." For example:

(Voicemail message) "Hi this is Josh...To delete this message, press seven to save
it, press 9..."

What causes these behaviors and how does one solve it?