I have read through a ton of forums on this matter just now.
From what i know:
1. you have to be in the USA (i think you are)
2. Blackberry, iphone and windows mobile versions of aim of the same version are supported.
3. Some people just said to get yahoo mail
4. Some people claim to know nothing about it and that for 2 years AOL haven't really helped
I've not used AIM in quite some time now, don't live in the US and I have never used it for phones
Sorry if i'm no help but maybe someone else will pop by and give you far better advice than myself.