
Asterisk is an open source system than runs on Linux and can be used with existing phone systems to integrate VoIP. If you want to learn more, don't miss
O'Reilly Asterix: The Future of Telephony offered as a
free e-book download [PDF]. Their server is currently terribly slow; perhaps they should upgrade from Microsoft-IIS/6.0 to Apache.
Related: Read O'Reilly Hacks Series books using Google hack
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