AOL (NYSE: TWX) has opened up its AIM messaging client, the biggest in the market, to third party developers, after years of trying to stave them off. Now services like Meebo or all-in-one IM clients like Trillian or Pidgin, can plug into the AIM service without resorting to hacks. Until now, these third party service would have to reverse engineer access to networks like AIM, Yahoo (NSDQ: YHOO), MSN and others, and be in a constant game of one-oneupmanship to keep the access going.

Wired News: The new OpenAIM 2.0 joins GTalk (Google’s chat network) in offering unfettered access to third-party applications and services. AOL is going even further, offering such services the option to run AOL-served ads as part of a revenue sharing plan, though details haven’t been released yet. More here on AOL’s developer page.