We can only apply iPhone skins when we are out doing another repair. The skin goes over the broken glass so you do not see it and are designed to look like the back of an iphone. 3 month warranty, but do last.
If you have broken the glass on the back of your iPhone there is currently only two ways to fix this.
Replace the entire housing, this is the safest and Apple approved way of sorting out the issue but is expensive.
Or get a company to laser the glass off the back. The glass is not designed to come off, the laser can cause damage to the internal parts of your phone, this is not recommended, but cheaper.
Now there is a third way. We can apply a skin to your the back of your phone that will cover the broken glass and to anyone else looks like the back of an iPhone.