To block incoming text or picture messages (SMS or MMS) or mark them as spam, follow these steps:
Using a text or picture message from the spam number
1.From any Home screen, tap Messages.
2.Touch and hold the conversation thread from the number you want to block.
3.Tap the Add to spam numbers icon in the top right-hand corner.
Using the Settings menu
1.From any Home screen, tap Messages.
2.Tap the MORE icon.
3.Tap Settings.
4.Tap Spam filter to select the check box.
5.Tap Manage spam numbers.
6.Manually enter number and tap the + plus sign or choose from Inbox or Contacts.
7.When finished, tap the back arrow.
I also discovered that you can read the spam messages (messages from an annoying ex) by going into Messages > More > Settings > Spam Filter > Spam Messages.
You can delete them or restore them to your regular text message inbox.
Good Luck!