iPhone backup restore SMS
If you used the iTunes backup restore process or the iCloud backup restore process, then your messages should have been transferred automatically back to your phone as these are included with the iTunes/iCloud backup.

If for some reason this did not happen, you might want to try restoring again or restoring from a different backup (if available).

Reference: http://support.apple.com/kb/ht4946

Note the mention of Messages in the list of data that is backed up.

iTunes will back up the following information 
    - Messages (iMessage and carrier SMS or MMS pictures and videos).