Replacing a cracked iPhone 4s screen may be easier than you think
It may look impossible to replace an iPhone 4 or iPhone 4s screen. Apple went to great lengths to make all versions of the iPhone look unserviceable. However, iPhone 4 screen repair turns out to be fairly straightforward if you have the right tools.
The video below shows the process to replace an iPhone 4s screen in good detail. Two screws, the back slides off, there's a few parts inside to deal with, and so forth. The screws in question are tiny, however, and will require the correct tools or you run the risk of stripping the screw heads.
That leaves the question of, well, where do you get the tools and the parts? Head over to eBay and the search phrase "replace iphone 4s battery" gives you several choices to find replacement iPhone 4s screens and toolkits. Simply make sure to select a kit that includes the tool. I see several kits in the neighborhood of $8.99.