Sims 3 won't have any online DRM protection at all.
From Rod Humble's blog:
"The game will have disc-based copy protection – there is a Serial Code just like The Sims 2. To play the game there will not be any online authentication needed," he said.
"We feel like this is a good, time-proven solution that makes it easy for you to play the game without DRM methods that feel overly invasive or leave you concerned about authorization server access in the distant future."
It's out in June.