How to use FaceTime over cellular data with straight talk?

I have an iPhone 4 (not s) and I use straight talk. I tried to FaceTime my friend and noticed you have to use wifi… Well I don't have wifi! I read you can go to settings, FaceTime, turn use cellular data on. But my phone doesn't say that! Idk why so yeah how do I get FaceTime to work?

Unfortunately FaceTime is not designed to be use over mobile data. However you can make it work on mobile data when you have jailbroken iphone.