So i am selling my ATT SSG2 to a friend who wants to use it and let his wife use his s3. Question is in order to use the S2 does he have to buy a sim from an att store to use it?? He is grandfathered into the unlimited plan and i think the s3 uses a smaller sim. So would the smaller one work in the s2 or does he have to get a brand new sim card through att to use it??