Firstly backup your iPhone text message using iTunes as usual. Once it's done, then navigate to the following path according your existing operating systems:
- For Windows XP – C:\Documents and Settings\your_name_here\Application Data\
- For Vista and Win 7 – C:\Users\your_name_here\AppData\Roaming
- For Mac – User -> Library -> Application Support -> Mobile Sync -> Backup – > [ID]
Within the folder, find a file with extension like this: .mddata or .mdbackup. This file is where your messages are stored. To open the file you can use textEdit for Mac or Notepad in Windows OS.
Then you can copy the entire text messages from your iPhone and save it to your computer for backup purpose.
Anyway perhaps this thing is less important for some users who don't feel in need to backup text messages, but for others there somehow they feel otherwise for keep their important text messages for certain reasons like password, codes or number in their SMS streams.
Via: iPhone Stuff 4 U.