I've never used Yahoo chat, but since rtcomm supports jabber it should be possible to use with jabber a server supporting several transports, including yahoo. There are several such servers, for example http://jabber.belnet.be/. Personally I prefer to have only one Jabber account that connects to all protocols I need. This is not only convenient (if I want to setup my chat on a new computer) but it also saves the battery (because the tablet connects with only one server).