TESO’s team stated via twitter today that beta sign-ups will begin in 2013. Sadly they haven’t said what part of 2013. However, seeing as how the game is slated to arrive the same year, I’m going to go out on a limb and guess we’ll see signups before June.
The tweet did say for people to look on the official TESO site as well as their various social outlets to find out when the beta sign-ups kick off.
The beta has officially been announced. You can read all about it here.