Here's a little cool trick for those who have a jailbroken touch.
If you have SSH installed go to
system/library/coreservices/springboard.app
and edit the N81AP.plist
and add the following lines
<key>sms</key>
<true/>
(you can also use iFile, if you don't have SSH)
Reboot your iPod touch, and voilà! You have the SMS app!
And if you restore your iPod touch from your iPhone backup, you will see your SMS on the app.
If you have SSH installed go to
system/library/coreservices/springboard.app
and edit the N81AP.plist
and add the following lines
<key>sms</key>
<true/>
(you can also use iFile, if you don't have SSH)

Reboot your iPod touch, and voilà! You have the SMS app!

And if you restore your iPod touch from your iPhone backup, you will see your SMS on the app.
