I used to do this before i purchased my 5. Keep your account on the GS3 LTE data plan as it will work just fine with the iphone 4s. If you have the iphone data plan the data services on your gs3 wont work. I hate apple for switching to a nano sim, as i enjoy using both devices. My iphone 5 now Serves me well as an ipod touch since the s3 is my daily driver.
Good luck!
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