How to get Front-Facing Camera Requiring Apps?

I only have an iPhone 3G, and I really want to play PvsZ2, but it requires a front facing camera! I haven't seen a need for it in videos, but even if there's, couldn't I just use the back one? Is there a way to still get it?

An iPhone 3GS might run it because it has the latest operating system, but I doubt it. Just upgrade your phone.