If you’ve ever received spam on your iPhone through Apple’s iMessage service, you can now report the message directly to Apple for investigation. It’ll require that you take a screenshot of the message and email it to Apple along with the sender’s email or phone number and the date and time of the message. You would send all of the information to email@example.com.
The upcoming release of iOS7 will let you block a phone number or email address at the OS level, but this tool will actually let Apple block it before it even tries to reach your phone.
Source: Apple Knowledgebase