A voice/fax/modem is a fax/modem with integrated Digital Voice Messaging. Voice/fax/modems are usually bundled with voice software. Some voice programs allows up to 999 mailboxes making voice/fax/modems good enough for large businesses. Most voice/fax/modems are able to discern between voice and fax calls and have an option to setup mailboxes to receive voice or fax calls.
You can also record out going messages, greetings and announcements. Some voice programs have an integrated fax program that can handle faxes (send and receive) and fax-on-demand. Most voice software packages have a Pager Notification option, which will call your pager when you have received a message. Business Audio voice/fax/modems have the ability to play WAV files and are usually bundled with more advanced voice programs.