Yesterday, some users reported that they were having issues with their sim cards not registering on their Dev Alphas when they upgrade to the new os which was pushed out yesterday. According to a tweet sent out by Tim Neil of RIM, these issues have been resolved.
"Those with SIMs in their #DevAlpha having upgrade issues.. Give it a try again and let us know. GLOBAL server configuration updates now LIVE"
Let us know in the forums if the updates is now working for you.