I received a text message from 45751 also have not opted in on this solicitation and have also just tried the reply "STOP" and will wait and see, No confirmation.
I looked back at the 1st text to they included their url (soylentblack.net), which I Googled and found this to be the company spreading this SMS spam.
Immediately I wanted to find out who owns this business (Me being a web developer) looked the domain up and found the following (Thanks to Network Solutions):
Registrant, Technical & Administrative Contact: Black, Laura
701 5th Avenue, Seattle, WA 98104, US
Google Maps didn't provide me with any business I knew of that operated out of this physical location. However Bing Maps mentioned Sirius Satellite R