I don't know the details, but I heard somewhere else on this forum that certain Nokia phones support AAC as well. This article mentions SE too. A web search for "Nokia AAC" seems to confirm this.
It will play AAC files, but note that I say encoded AAC files, which I don't believe it will. Besides, the nokia cell phone is far afield from a boombox..
As AAC is not a proprietary format, I find it baffling that more people aren't doing this. Sony, of course, is trying to push their format (hellooooooo betamax), but I don't know why I don't see every other boombox sporting AAC compatibility.