updated 09:18 am EDT, Mon April 21, 2014
Some users may be forced to upgrade or choose new AIM ID
As of June 30th, Apple will be discontinuing AIM iChat login support for users of OS X below v10.7.2, according to a new support document. The decision specifically affects people using a mac.com or me.com address as an AIM ID to sign into iChat. To get around the issue, people must either create a new AIM ID -- which will also require reentering contacts -- or upgrade to a later version of OS X.
More recent editions of OS X have dropped iChat entirely, replacing it with Messages, which syncs with iOS. Apple will likely phase out support for iChat once the app is no longer used by a significant number of people.