They cannot bill an owner of an iPod Touch. It has no cell service and relies on WiFi for it's connection. When AOL says their service is free, they mean they themselves won't charge you to use their service. If you have their AIM messages being forwarded to your cell phone however, they arrive as an SMS message, not as an instant message unless you happen to be logged into the AIM software and actively running it at the time you receive the instant message. The AIM app cannot run in the background. When you are logged into the AIM app, you receive an Instant Message (not billable). When AIM is not actively running, you receive an SMS instead (assuming you have forwarded your AIM messages to your cell). It even warns you when you enable the AIM forwarding service that service charges may apply from your cell provider for SMS messages.
As to what Apple is doing, they seem to be crossing a line at times with their policy regarding allowed apps. All I can say here is that they need to watch themselves. This is a new day and a new administration and Apple is already in their sights as well as AT&T when it comes to anti-trust.
I love Apple products, but they seem to be going too far in censoring applications and data on the iPhone. I am fully capable of deciding what is appropriate and what is not appropriate on my phone. If they have a legal commitment to AT&T that forced this then I would say they are making bad decisions that reflect poorly on Apple and hopefully they will do better in the future.
For those stating that 3g lag doesn't affect VOIP (yes I know this Google Voice is not a VOIP app but I couldn't resist), average 3g lag runs in the 1000 to 2000 millisecond range. That's 1-2 seconds to the laymen. It is undeniably noticeable. You get what you pay for. I don't see why cell providers are so afraid of VOIP apps, especially over 3G. The typical person would still use a cell service instead of VOIP due to lack of technical expertise or even knowledge that VOIP exists, lag, and bad connection quality. If you doubt it, you can download a free app called "Speed Test" from the app store which will report average ping times to a local server. You may be surprised at how poorly 3g performs in this respect.