Other posters report they have had success in forwarding these illegal texts to 7726. They are picked up by your cell phone carrier who will ask you to send them the phone number so they can investigate and have spam filters installed to block the texts. The following article tells you everything you need to know:

Security company Cloudmark created a spam messaging reporting service that nation’s major wireless carriers agreed earlier this year to start using. Now, customers of AT&T Mobility, Verizon Wireless, T-Mobile, Sprint and others can forward their text spam message to 7726. The mobile phone carrier will ask customers for the phone number that’s linked to the spam message so they and Cloudmark can start investigating.

http://www.ajc.com/news/business/text-spam-messages-on-the-rise/nSW3C/