I had the same problem and just patiently kept re-entering my phone number, zip code and ss#. A few times it got me to the screen where it asked me to choose my data plan, then I clicked continue, and then it said Session Time Out.
I kept trying and trying and eventually (after 2 hours) it worked.
Don't give up! And don't double click the "Continue" button or you'll be reset. You know what I mean? If you click continue and it looks like it's doing nothing, just wait patiently.
I used Chrome.
http://twitpic.com/1wy3kx
-@joshheller