How does everything fit into an iphone?
No the data won't delete from the iPhone unless you reset everything
How much does in cost a month for unlimited everything for an iPhone?
About $100 to $130 every month
Why does everything I download also download onto my wifes iPhone?
Can iPhone Sim Cards be swapped into another iPhone If so what is the process after you put the Sim in the other iPhone?
Yes it can be swapped. I actually swapped my razr's sim card to my iphone. Nothing happened. It works perfectly.
Do you have to plug in your iPhone 4S to download everything from your previous iPhone?
Yup, all you have to do it plug it into your computer and open iTunes and sync everything.