AOL Instant Messenger does have voice chat, but only with other IM users. AOL itself DOES NOT have the ability to voice chat or swap files with AOL IM users. Knowing people that have AOL, it seems to me that IM has much more functionality than AOL does. Strange, seeing as how they come from the same company...
(You have to select another IM user in the buddylist, then push the "talk" button below the names.
Make sure you have a good microphone. The iMac's built in one works fine, but I found that I could hear myself and the other person's replies through the speakers. I'm using 3.5.791, so maybe the technology was improved with the latest version.