When this tweak is activated it will reply to any text that you receive on your iPhone. You don’t need to click send button it will automatically send the selected message to the person.You should note that this tweak will use SMS messages from your carrier’s plan. So if you have limited SMS plan then use this tweak carefully.
AutoResponder tweak is available in Cydia under BigBoss repository. It costs $1.49 USD. You will need to have a jailbroken iPhone to install this tweak. If you don’t have a jailbroken iPhone then simply follow the step by step instructions posted here to jailbreak your iPhone on iOS 4.2.1 with Redsn0w.