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If you have friends using any program that supports SIP, XMPP or Gtalk networks, then you will want to install an all-in-one solution, which will be Gnome's
Empathy. Although Empathy supports Jabber, MSN, IRC networks (plus the ones that are supported by Pidgin), audio and video support is limited to SIP, XMPP and Gtalk networks. The instant messaging programs that use SIP protocol are Nimbuzz, Kcall, Kphone and Fring to name a few. A few examples of programs that use XMPP are Digsby, Meebo, Miranda, Proteus (Mac OS X only), Joost and Google Talk.