You have to sign up by the end of the month. I signed up on the web page on Sept 10th and never heard anything. Called two night ago and was told it came up with an error of customer not found. Puzzling as they had my name, home address, e-mail, and phone number yet nobody bothered to contact me about whatever the problem was.
Anyway, I did the deal over the phone, and was switched the next morning. You might consider doing it over the phone to be sure you make the deadline. 1-877-301-0314
This is better than the MCI deal I had once to get 25K miles for a year. Plus, Sprint is actually reputable unlike MCI/Worldcon! 😛