After reports that some sms messages were being displayed in the wrong order after installing the latest 1.1.3 iPhone update, Apple have posted a solution – turn on the automatic date / time updates!. Apparently this occurs when the internal clock doesn’t match up to the carrier clock. Anyway, here’s the solution:

• Make sure iPhone is setup to receive the network time. Choose General > Date & Time and turn Set Automatically to ON. (Note that in some locations, network time may not be available and in some cases, you may not see this option).
• If the issue continues after turning this setting on, the issue may be occurring because messages are being sent in quick succession (more common if the messages consist of only a few short words).

Link: Apple sms fix