iOS 7 now allows you to set up a list of numbers that you do not wish to receive calls or messages from. Numbers can easily be added to this list simply by selecting a contact card from your recent calls, messages, or contacts and tapping the Block this Caller option at the bottom. A single block list is shared by the Messages, Phone, and FaceTime features, and adding a number to the list will block you from being contacted from that number by any of these methods.
You can view the list of blocked numbers from within the iOS Settings app by selecting Blocked from the Phone, Messages, or FaceTime sections; as noted above, however, the list is shared across all three of these services, so these are just three different ways of accessing the same list.
Messages and FaceTime calls from blocked numbers will be ignored entirely; Phone calls will be sent directly to voicemail, but any resulting voicemail messages will be stored in a separate “Blocked Messages” section that can be found at the bottom of your visual voicemail message list.