Dterm 80 is the phone type, we need the model of the phone system it connects to which in turn will help determine if we can what model voicemail you have.

Any paperwork at all regarding purchase of this system? If not you may try taking pictures of the system with the front cover off, close up of the circuit card on the right side and posting them here.

I know you don't want to hear this but the chances of resetting the passwords is slim to none.

20 years is a long time, its way past time to upgrade.