A kernel works as a bridge between software and hardware. According to me when you turn on your s4 the capacitive buttons dont turn on but after the end of the bootscreen the buttons turn on this means that the kernel has setup his bridge between your software and hardwar.
Now flashing a custom kernel dont solve network issues. It gives additional functions like overclocking the device speed, decreasing or increasing heap size etc.
I think you should flash a custom rom which supports 2g. There are many roms available for your device.
Sent from my GT-S7562
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