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http://www.richard.neill.hemscott.net/voip.html
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http://dev2dev.bea.com/pub/a/2005/09/introduction-sip-part-1.html
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http://www.directcentrex.com
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http://www.grynx.com/index.php/projects/build-your-own-chat-cord
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http://www.rowetel.com/blog/?p=27
linphone + iptel
http://www.cure.nom.fr/article.php?theme=Linux&id_fic=23
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http://groups.google.com/group/low-cost-ata/topics
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http://people.via.ecp.fr/~alexis/asterisk
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http://www.gizmoproject.com
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http://www.grynx.com/index.php/projects/voip-for-free-with-the-sipura/1