As I read the SIM-Multi-Messenger fits the interests of the users, to have "The Others" (Lost) Friends as well under the GUI.
Maybe then SIM-Developers wants to add VOIP and Video-Chat or you can, if it comes to the case, add it later in one or two years to the serverless Message Window of the Retroshare Messenger.
Maybe better than SIP (Text-Stream) is the compressed H323-Standard for the OpenSSL connection and I found in another forum this overview of a c++ H323-Library, especially Openphone or TStone sound interesting...
so keep the links in mind:
Comparisons between H.323 and SIP
http://www.packetizer.com/voip/h323_vs_sip/complist.html
Open Source C++ Library SIP
http://www.sipfoundry.org/reSIProcate/
Open Source H.323 c++ Library
http://www.packetizer.com/voip/h323/
http://www.openh323.org/code.html
http://sourceforge.net/project/showfiles.php?group_id=80674
http://www.en.voipforo.com/H323/H323_objetives.php
Openphone H323
http://www.openh323.org/bin/openphone_20030313_win32.zip
http://www.openh323.org/bin/openh323_20030313_win32.zip
http://www.openh323.org/bin/pwlib_20030313_win32.zip
Source of Openphone Windows
http://www.openh323.org/bin/pwlib_1.5.2.zip
http://www.openh323.org/bin/openphone_1.9.1.zip
http://www.openh323.org/bin/openh323_1.12.2.zip
http://www.openh323.org/bin/ohphone_1.4.1.zip
Source of Openphone Unix
N/A
requires OpenH323, PWLib
http://www.openh323.org/bin/openh323_1.12.2.tar.gz
http://www.openh323.org/bin/pwlib_1.5.2.tar.gz
http://www.openh323.org/bin/ohphone_1.4.1.tar.gz
p2pPhone TStone.sf.net
http://downloads.sourceforge.net/tstone/p2pvoip0.9.zip?modtime=1138416222&big_mirror=0
Tapioca Phone libraries
http://tapioca-voip.sourceforge.net/wiki/index.php/Tapioca
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http://dev.openwengo.com/trac/openwengo/trac.cgi/wiki
http://dev.openwengo.com/trac/openwengo/trac.cgi/wiki/GetTheSourceWengoPhoneNg
http://download.wengo.com/releases/WengoPhone-2.1/RC2/sources/WengoPhone-2.1-rc2.src.tar.bz2
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as well this threads belong to here
http://iaxclient.wiki.sourceforge.net/
http://sourceforge.net/forum/forum.php?thread_id=1840581&forum_id=618174
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