With the launch of iOS 7 which is expected to take place later this year, one of the features Apple will be introducing is the ability to block Apple IDs from iMessage or FaceTime. While the messages can still be sent as regular text, it can help block spammers or maybe that stalker ex of yours. In any case in the meantime it looks like Apple has already begun offering iMessage spam reporting, thanks to a new knowledge base article found on Apple's website.
Ubergizmo , Apple Introduces Spam Reporting For iMessage, Apple Introduces Spam Reporting For iMessage
