How to restrict cellular data to imessage only? (Iphone 4)?

I would like to use my 3G cellular data only for imessage when not using Wi-Fi for the iphone 4. I don't want to use it for anything else like other apps, web browsing, notifications etc. Is there any way to do this or am I screwed? If it matters I have a 1 GB monthly data plan.

If you jailbreak your iPhone there's an extension you can download called 3GUnRestricter, which does just that. But since I see your doing this on iOS 6 I'd recommend not jailbreaking for the time being, since it is a tether jailbreak (a more restrictive jailbreak). Wait a few months and google "iPhone 4 jailbreak for iOS 6" if its an untethered jailbreak, then, if its still a bother for you, go ahead and jailbreak and download 3GUnRestricter.

Sorry if thats a tad confusing. But with the regular, unjailbroken iOS, that is impossible.