What "P" was suggesting was that they didnt program the key correctly. To programm the key you need to get into programming at trans 800 then password +1 then speaker key and dail 722 or if all of them are the same 723, press the vt key and put the voicemail group number in as an extender next to the vt ie 529 or what ever the group is

or like "P" said get them back out to program it