There are times when leaving a message for a group is counter productive. This includes when groups are not staffed or the group is forwarded to a land line that does not have a voice mail attached. In the second scenerio, if the landline is not answered the call comes back to the Vocera group and a voice message is left for the group. This defeats the purpose of having a landline without voice mail. There are times where this is not only acceptable but preferable.
The option to disable group voicemail was added in Voice Server 5.3.0