Issue or symptom
When sending or receiving text messages on the iPhone, the SMS messages may be displayed out of sequence.
This can occur if the iPhone is not displaying the same date and time setting as the carrier network time.
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).
This document will be updated as more information becomes available, please visit apple.com.
source: apple .com