The Bizfon 680 is a popular small business phone system. The Bizfon 680 was designed to be as simple as possible for users to set up and configure. The simplicity of the phone does come with some drawbacks, however. Many features that would otherwise be standard like multi-tenant configuration are absent from the Bizfon 680 to make it easy to program.
Voice Vault Cards
To address the shortcomings of their system, Bizfon released a set of add in cards for the Bizfon 680. These memory cards add additional 2 hours of voicemail greeting time or 4 hours. In addition, one card in particular can grant the multi-tenant capabilities missing from the Bizfon 680 originally.
These cards install in the top of your Bizfon 680. Under a panel you should see the slot where the Voice Vault flash cards are installed.
*CORRECTION UPDATE June 2015 - Thanks for your informative comments Cecilia!