Java VoIP servers:
http://ask.slashdot.org/article.pl?sid=01/03/21/0713247

Demon's VoIP:
http://www.google.co.uk/search?q=demon+voip&hl=en

OpenH323 source code:
http://www.voxgratia.org/downloads.html

IANA RFC standards submission instructions to authors:
ftp://ftp.rfc-editor.org/in-notes/rfc-editor/instructions2authors.txt

Sun "Java Media Framework VoIP" search:
http://onesearch.sun.com/search/onesearch/index.jsp?qt=Java+Media+Framework+VoIP&charset=utf-8&col=developer-reference&cs=false&rt=true

OpenH323 standards documents (including comment on prohibitive "availability"):
http://www.openh323.org/standards.html

Discussion of VoIP project on DevX's forum:
http://forums.devx.com/showthread.php?t=143032

Wikipedia OSI model:
http://en.wikipedia.org/wiki/OSI_model

Transport Protocol for Real-time Applications (RFC3550):
http://www.packetizer.com/rfc/rfc3550