I got the same message just now and reported it to AT&T.

I received on my phone a text that read:"You have been selected to receive a FREE Best Buy gift card... etc." from 562-879-5804--a cell phone with no voicemail box. This is SPAM. Nothing is given unsolicited, except spam, so there!  I did try to research the webiste but my firewall blocked access. My security program probably has it listed as a dangerous site. So let all beware of UNSOLICITED text messages for "Free" stuff because nothing is free. And this "Best Buy" text has originated from other cell phone numbers with no voice mail boxes, too.