Switching from an iPhone 4s to an iPhone 4?

I broke my iPhone 4s and my friend is selling me his iPhone 4, will the sim cad fit in there, and will I it automatically have all my stuff on there e.g. Messages pictures etc. And will I still have my contract (unlimited free texts and internet?)

Your sim card will fit, but only your sim card contacts will transfer over. The messages and other stuff will have to be either restored from a backup or transfered manually. You can see a comparison of both phones just in case you wanna