The biteSMS app runs on jailbroken iPhone and iPod devices. Wait! Don't go yet! Jailbreaking is now completely legal and very easy. It doesn't harm your device in any way, and you get to use great apps like biteSMS.
So, getting biteSMS onto your device is two simple steps:
Jailbreak your iPhone or iPod device, which takes about 10 minutes. Next!
You download biteSMS from Cydia. Cydia is an app that gets installed automatically as part of the jailbreak. It's like the App Store, but for jailbreak apps. In Cydia, just search for biteSMS and click the Install button. Done!