Vgetty turns your voice modem into an answering machine. It adds voice capabilities to mgetty. This means, that you can handle data, fax and voice calls on one telephone line.
HylaFAX™ is an enterprise-class open-source system for sending and receiving facsimiles. This is the place where users can find HylaFAX+ support, work, and releases. The "+" means that it is better.
IAXmodem is a software modem written in C that uses an IAX channel (commonly provided by an Asterisk PBX system) instead of a traditional phone line and uses a DSP library instead of DSP hardware chipsets.
The gnu.hylafax package is a pure-Java implementation of the HylaFAX (FAX server) client protocol. The gnu.hylafax package can be used to implement a HylaFAX client that will run on any Java-supporting system.
Having a digital ISDN telephone connection lets you easily integrate Fax and Answering Machine functionality into your Linux server. SuSE (and Debian) distribute a package called Capisuite for this purpose. You will also need a supported ISDN card (an AVM Fritz card is inexpensive and works).