Alright. However will it not be an issue if I mix the stock firmware with a custom ROM running LP? Stock runs with JB if I remember correctly. When I flashed stock I just reverted to my NAND backup that was made from the software that came with the phone yeah. My country (ZA) and region, Vodacom branded version of Touchwiz.
I'm gonna try my SIM in a different phone and vice-verse later today to see if it may be related to the SIM card somehow. I've used all the different available APN settings for Vodacom SA and nothing works. I firmly believe this is a firmware problem though, seeing as that my stock ROM with APN settings that used to work also don't work now.
Not sure what you mean about mixing firmware as you can only run one or the other. But I'm thinking maybe try searching http://www.sammobile.com for the latest matching firmware, flashing that 2 times. Testing data . Then try a custom recovery and LP rom. I would wipe system when flashing LP.
Is what I would do... I think you might have better results flashing from the latest compatible stock kit kat firmware.
BE WARNED! Your boot loader will most likely be updated to the latest version also, maybe KNOX enabled. Don't know how this will affect the i9190 but on i9195 it wasn't an issue.
You could do with advice from someone with your device. This isn't really the best place for this as it's not really this roms issue. Try opening a separate topic from q&a. You might get a better response.
I wouldn't act on my advice until your 100% sure as I doubt you can undo bootloader changes.
Best of luck!