How can I report / block spam text messages on my AT&T iPhone?
To report a spam SMS message received on your iPhone, you can forward the text to the number SPAM (7726). AT&T will reply with a text asking for the phone number of the person who sent the spam text message.
Reply with the phone number and that's it. Text messages reported as spam and the replies from AT&T are not counted towards your data plan or monthly text allowance.