There's not a lot of detail on this, but AOL will be launching some sort of VOIP service linked with AIM. The service will offer a unique, free phone number where your friends and relations can leave messages. We doubt very much that this is a unique phone number and that instead they've created a call center to accept voice messages via an 800-number and PIN combo.
The incoming calls are transferred through the AIM service and for $14.95 you can make unlimited calls to anywhere in the US.
AOL to launch free AIM phone service [News.com.com.com]