Sim cards #2

question::
sim cards are the things that hold your pictures and info. in the phone right?
the sim card is located in the back of the phone correct?
I need to know if there is a difference between sim cards and phone...please explain 2 me. asap!
and...

with the difference of the phone would it make the sim card cost differently??

The simcard stores Phone contacts, and has the ability to hold a certain amount of Txt messages.
a lot of phones however are capable of holding a memory card, which stores music, photoes, videos, etc. The phone memory can hold contacts, text messages, photos, music, videos, etc.

I had a prepaid phone for att and the sim card pretty much was the phone. if the sim card wasnt in you couldnt do anything not even turn on the phone or a screen would come up saying sim card absent