from a WikiHow article :
http://www.wikihow.com/Block-Mobile-Phone-Spam
"The most important thing you can help stop text message spam is to reporting it to your carrier. Carriers shut down and block spammers, often suing the worst offenders. But they need you to tell them who is spamming and what is in the spam messages. To report text message spam, forward the text message to short code 7726 (spells 'SPAM' on the keypad).
from AT&T :
http://www.att.net/smartcontrols-SpamControlsForWireless
i just having been getting rated xxx from this person texting me, it says it is a landline in los angeles california then they dialed my number and hung up, i told them ( text that iam married) they say they are a lesbian woman. its very obscene. and iam married