This is from a company called "Bigger Bidder" - In this particular case, you're directed to a site where you can compete with others to bid on a $1000 Best Buy gift card (The opening bid is $0 - Free, of course it won't be by the time it's given away). While technically "SPAM" the company appears to be legit. Also, from their Privacy Policy, "To opt-out from receiving any additional SMS text messages simply reply to any text message you receive from us with "STOP", "QUIT" or "END"."