How to not have the text conversation show on the lock screen (iPhone 4)?

I have friends who have an iPhone and when they get texts the conversation doesn't show up on the lock screen it just says "Text message" so people can't look over and see the convo. How can I get this on my phone? I Have the iPhone 4.Is it even possible or do I need a 4S?

Open Settings > Notifications > Messages > Swtch "Show Preview" to off.

There's honestly, little differences between the iPhone 4 and the iPhone 4S, except the camera and some other small upgrades. So no, you can do that with the iPhone 4 as well, but I don't know how. I suggest going to settings and looking there. If you can't find it, then maybe ask one of your friends who has it if she could change it for you.