There are two free softwares that support AIM.
WebMessenger software allows you to access to AIM, Google, MSN Messenger/Window Messenger, ICQ and Yahoo from your BlackBerry.
Here is a link: WebMessenger Inc.
Bing software also allows you to access up to 3 apps.
Link encloses: bing - your mobile room for good friends - Home
JiveTalk remains to be a superior IM software.
Ramble software is S U CK for sure!