Scam? Unwrap a Year of Wireless Sweepstakes

I received a call last night from "Ellen" with The Story House saying I had won a year of free wireless service as an entrant in one of your recent sweepstakes.  She followed up with an email with several documents that I need to sign and return within 3 business days.  I recall registering for a sweepstakes, but can't remember if it was during the timeframe listed in the documents.

I was only able to open one of the documents (official rules) and it was on plain white.   It does list ATT Mobility LCC as the program sponsor and the Story House as the Program Administrator.

Is this legitimate?  They are requesting completion of a W-9.  I don't want to disclose my Social Security # if this isn't legit.

Thanks!