Just happened to see this thread because I am researching this Model to possibly use on Metro PCS /TMobile in USA.
SGH i257 IS the model number.
This is an upgrade over most S4 Minis because it has16 GIG ROM versus 8 in other versions.
There are also more frequency bands in this version enabling it to unlocked and (hopefully) get full speed with many Carriers .
This is also used by AT&T USA.
There are no different Cameras, and all ,S4 Minis have dualcore 1.7 GHZ. CPU and 1.5 GIG RAM.
But yours has an extra 8 GIG ROM .