Get a good case and you won't have to worry about it. I recommend the Otterbox Defender. Apple will charge $150 to replace it if you break the glass. The front glass is somewhat difficult to replace and the back glass is extremely easy to replace yourself. An OEM backplate is $80 if you'd rather do it yourself. The front is more. Another option is to get Apple Care+. It costs $100, but Apple will replace it for $50 when you have Apple Care+. You have to buy it within 30 days of purchase of the 4S, though. There are other benefits to it as well.