The Inquirer reveals the reason why AMD renamed Socket M2 to Socket AM2:
We managed to get confirmation that AMD actually had some copyright problems and that it could not use socket M. The alternative was to add an additional letter A and everybody was cool with that.
As a big company you don’t want to mess with copyrights and since we are still talking about unannounced products, AMD didn’t have any problems renaming it. We will all get used to it as much as we found it pretty easy to call the Hammer CPU Opteron. It can not get worse than that, I guess.
This new socket will launch on 666 (June 6th, 2006).