Comparing to bitesms, GO SMS is free and with no ads. And the UI is well designed and the quick reply is very useful. More and more functions will be added and it's good to have a try. You can download GO SMS from Cydia by searching "gosms". It's hosted by the Bigboss repository. For iOS 5.x user, it can be used in both iPod Touch and iPhone. For iOS 4.x user, it can only be used in iphone since SMS capability is required.