disableEmergency is a new Cydia tweak that lets you disable the emergency call button on screen lock. This app adds an option to Settings.app which lets you toggle it on or off. This tweak won’t allow you to make an emergency call in case of a real emergency too so we aren’t really sure why anyone would want to risk that. But it’s a choice you get and choice is all what jailbreaking is about.
disableEmergency is available in the BigBoss repo for free. You’ll need a jailbroken iPhone to install this tweak. Follow our guides for Mac and Windows. You can follow this guide to jailbreak iOS 4.2.1 on iPhone 4 without updating baseband.