AIM works anywhere (except maybe a few draconian countries who could be blocking it. Dunno if it works in China, etc.) The Blackberry, well, that's another matter, has to have the proper wireless service providers, etc. I don't know much about using those outside the US.

One thing also of note here is that your AIM settings and buddy list are stored at the server. That means if you sit down at a PC somewhere and sign onto AIM, you'll get the same buddy list and blocking preferences and such that you do at any other place you use AIM including on the Blackberry. (I have a T-Mobile Sidekick which has AIM and all my settings remain intact when I sign on from it.) If you're at a place where you can't or don't want to install the AIM client software, you can use AIM Express, which works through a web browser interface (uses Java). Just head to http://www.aim.com/ It's not ideal, but useful in a pinch.