If you want to write Thai, here is a guide:
http://www.iphone.in.th/iphone/index.php?showtopic=2444
Also in Thai but it is quite easy to do.
1. Download
http://www.4shared.com/file/25156557...yboardmen.html and unzip it (you will need it in step 8)
2. Install App Tapp Installer if you don't have it already.
3. Go to
http://www.russianiphone.ru/beta/en/ with
your iphone
4. It will prompt to install a package, install it.
5. Restart your phone
6. Launch Installer and go to Localization and install Mobile Enhancer version 1.0a3
7. Restart your phone
8. Copy the folder "cyrillic-keyboard.men" you unzip on Step 1 to /Library/MobileEnhancer (scp -r /path/to/cyrillic-keyboard.men
root@your.phone.ip.address:/Library/MobileEnhancer)
9. Restart your phone
10. Switch to Thai and English using the .?123 button at the bottom left.
11. Enjoy!
It takes about 5min to do.