There are demo scripts rpc_client.pl and rpc_server.pl in the original distribution of Net::Jabber package to demonstrate Jabber RPC functionality. Those samples don't work, because rpc_server.pl uses Net::Jabber::Client::RPCSetCallBacks() to set user subs for call processing.

RPCSetCallbacks() doesn't really do anything, but prepares some internal data structures, while real work is performed by Net::Jabber::Protocol::callbackInit() (Net::Jabber::Protocol is inherited by Net::Jabber::Client), which is supposed to override the same sub in Net::XMPP::Protocol (also inherited by Net::Jabber::Client through Net::XMPP::Client).

So I believe there is a problem with definition of Net::Jabber::Client, but I'm not good enough to fix it myself :-)