Direct Path for iPhone SMS directory files (sms.db)

var/Mobile/Library/SMS

Export iPhone Text Messages to a Spreadsheet

Here's one messy way to do it:

1. Jailbreak. First, you'll need to jailbreak your iPhone using these instructions (here's the Windows user version). Make sure you install OpenSSH (here's how) to make your iPhone accessible via SFTP.
2. SFTP into the phone. Go to the phone's network settings, and view the details of the active connection. Write down the device's IP address. Using your favorite FTP client, SFTP into that IP address using the username root and password alpine.
3. Download sms.db. Your text message database is located in /var/mobile/Library/SMS/sms.db on your iPhone. Download that file to your computer.
4. Open the SQLite database. That sms.db file is a SQLite database, which you can edit and view using free tools. Download one of those tools—the SQLite Database Browser—and install it on your computer. Open up the sms.db file, and click on the Browse Data tab. Choose the message table and you'll see your SMS history, and it'll look like this:
5. Export to CSV. From the SQLite Database Browser's File menu, choose Export > Table to CSV file. Save the resulting comma-delimited file, and open it using your spreadsheet of choice (whether it's Excel or OpenOffice.org).

ref: http://lifehacker.com/399631/export-iphone-text-messages-to-a-spreadsheet