For the default Chat application I haven't seen Yahoo yet, and I never understood the difference between AIM and ICQ...

Pidgin has been ported though and is currently *tested* in the "Extras-Testing" repository/catalogue.
Note that software in Extras-Testing IS NOT meant for end-users as software can drain your battery, destroy your data, ...
Wait until Pidgin has reached "Extras" instead after having made sure that it's "safe".