I've been using a hacked version of the 'old' Windows Mobile AIM client (2.0.17) for England which can be found here:
http://info.aol.co.uk/aim/wince/index.html
It works just fine for accounts on AIM that were started in the United States. It was just offered, for a time, on the aol.co.uk website and there was no official client on the main
www.aol.com website.
The hack moves the Windows task bar to the bottom of the screen when you're in the application because otherwise some of the options don't work correctly (from what I remember).
Anyway, I use it and like it for its simplicity. I only log in to AIM when I want to chat and then turn it off when I don't. I don't want it integrated with my whole today screen, etc. and for that .... this application meets my needs.
Today, AOL actually has an official (in the United States) client for Windows Mobile here (which I don't like. There is too much bloat for me):
http://beta.aol.com/projects.php?project=aimwinmobile
I'm going to attach the 'hacked' cab I use to this post.