It is pretty simple to repair your broken iPhone screen, there are multiple instructions about it on the web. Just google your specific type of phone. Inspired by my friend gaiageek I used these instructions and it worked really well:
I admit, it was a bit nerve wrecking and I had my repair-it-all dad with me who is more specialised in cars and was amazed himself that we could repair a smartphone. But with time, humour and the right size screwdriver we made it. It is also a good idea to consider replacing the battery as this is only a few more steps and can increase your phones value.