Hello sorry for the questions but I'm even more confused!

Even though I log in using a .mac name, my buddy list says AIM Buddies..can I chat to AOL Instant Messenger users if I'm logged in via a .mac name ?

Having researched some more, I see most suggesting that people get an AIM account as it is free. Is there a reason not to get the 'free iChat account' that ends up being a .mac? It is free isn't it?