According to this DailyTech article, AMD will no longer be using “Athlon” as the name of their highest performing processors and instead opt for a new moniker, “Phenom” short for phenomenal. The Athlon will be handed down to the second tier of processors or the middle line and then the Sempron will be kept for the lower end products.
This is the second name change that I’m aware of. Prior to a few years ago, the Sempron was known as a Duron.
I just hope that AMD will regain the performance crown come July/August when their new processor is supposed to debut.