The biteSMS application is installed from Cydia, available on all jailbroken iPhones. From the iPhone home screen, you only need a few taps to install:
Tap "Cydia" to start it:
Tap the "Sections" button:
Scroll down to the "Messaging" section and tap it:
Tap "biteSMS":
Tap the "Install" button:
And finally tap the "Confirm" button: