Just click on either "new customer" or "add a line" then search for the Galaxy S II, add your voice/data plan and checkout and you will see a 50% off promo applied ($99 off) + the activation fee is waived + free overnight shipping.
This deal doesn't work for upgrades so this seems like just for new customers and those that want to add a new line to their family plan. For upgrades you would want to go through Amazon Wireless for the best price $150 tax free.
I just went through the whole process but did not actually check out, and as a "new customer," the promotion worked. I'm currently a Verizon customer, but I get a really weak signal at my house (where AT&T gets a good signal, according to my neighbor), so I am thinking about switching over. I kind of want to wait til November 11 to see what the deal with the Nexus Prime is though...
I've been trying all day to get this to work for me.. but I don't think that it will. I think its not working as someone said before because I have a business account.. because of the discount I am receiving.. SUCKS @$$