Waa,
Actually, since iChat uses your Address Book to store your buddies you can simply enter their names there and they will be displayed in your Buddy List.
Egor,
Whether or not AIM has a large installed base outside of the US, I do not know, however, AIM which operates independently of AOL and in conjunction with the Netscape and Compuserve brands is certainly global and a fine choice for anyone looking for Chat/IM/PTP.
iChat alternatives for chatting in OS X