As many have discovered, it is actually just the I9195 with different firmware. One noticeable difference is the lack of a FM tuner
If you have clockworkmod setup on your I257m,
(if you dont, ODIN flash recovery-clockwork-188.8.131.52-serranoltexx.tar ... info here)
you can install the following zip,
which has the HybridRadio.apk and libfmradio_jni.so files from the I9195 rom.
NOTE: You need a I9195 kernel (or if someone can mod a stock i257m kernel) installed in order for the Radio app to run!