Do not respond to unwanted texts or emails from questionable sources. Several mobile service providers will allow you to report unwanted spam texts by simply texting/forwarding it to 7726 (or “spam”) to enable the providers to prevent future unwanted texts from the specific sender.
More info:
http://en.wikipedia.org/wiki/Mobile_phone_spam
http://blog.usa.gov/post/89152807112/protect-yourself-from-text-message-spam
However, in many cases, the text origin, as seen on your phone, is faked. The internet domain does not exist, or the phone number may have been spoofed.
This number and man with a heavy accent has called my cell phone numerous times from the "medical reimbursement department" - - this time I asked him from what company and he told me he wanted to hire me for tonight - - ME: "Hire me, Hire me for what?" He started to become explicit with what he wanted to hire me for - - -