If you've upgraded your iPhone or iPad to iOS 7, you've probably already noticed that the Messages and Mail apps both default to only showing the first name of a contact in a conversation thread. For those of us that have more than one John in our contacts, it can get pretty confusing. Fortunately, there's a way to turn last names back on by default.
That's all there is to it. Your Messages and Mail apps should now show last names again if you've got them listed as such in your contacts. Any other native apps that use name shortening will also stop doing so.