If you’re rocking a US Samsung Galaxy S III variant and would like to expand on either your 16GB or 32GB worth of storage allotted for apps and games, you might want to have a look at this mod from XDA Senior Member, and our dear friend, zedomax.
Max has managed to develop a mod that allows you to swap internal storage with your external SD card so you can increase your app data storage.
Originally, mattiadj released a version of this for the international Galaxy S III (i9300), but it was incompatible with all US variants until Max got his hands on it and worked a bit of magic. He also added a code that disables the mod when you remove your microSD card from the slot, forcing the default storage location to change back to internal.
Best of all, the difficulty level to apply this mod is as low as it gets. All you need is a rooted device, a custom recovery, and the zip file from the original thread. Flash the zip in your recovery and boom — simple App2ExtSD2 for your Galaxy S III. Now you can download all the games and app your microSD card can handle.
Before you can use this, you will need:
1) Rooted Galaxy S3 (SCH-I535/SPH-L710/SGH-T999/SCH-I747) or also Canadian versions too (i747m, etc…etc…)
2) A ROM/kernel with init.d support!
3) I’ve only tested this with TouchWiz-based ROMs, so it should work on stock ROMs and any TouchWiz-based ROMs, not sure on CM9 or CM10.
4) You must use the FAT32 or EXTFAT zip file below, depending on what format your microSD Card is in! (e.g. if you have a FAT32 microSD card, use FAT32)