!! Be aware, I have tried the following procedure and am using S5 Elite Lite ROM by MaHo_66 !!
To start the unlocking procedure, first see if your device is actually sim-locked by inserting another sim-card from another provider and see if it asks for a code. If it asks, press on dismiss. Now, the actual steps:
- Take a note of your CSC and MODEM with the help of Phone INFO.
- Download from my GDrive I9305XXALI5_I9305EVRALI5.zip and copy it to either an USB OTG drive or to a MicroSD card (if you have one).
- Make sure you have a custom recovery installed. Boot into it with the VOL UP+HOME+POWER button combination and make a nandroid backup of your current ROM. Make sure to do it on the MicroSD if you have one.
- Go and do an advanced wipe and only wipe the following partitions: Cache, Dalvik Cache, Data and System.
- Now install the zip file you previously copied on either an external USB OTG drive or on the MicroSD card.
- While the rom is booting, search around on XDA for the aforementioned CSC code and a suitable modem for your BACKED UP rom.(The ZIP file I provided you will have changed the modem and CSC, so make sure you noted the CSC and modem before)
- After the rom is done booting, skip the set-up wizard and the network lock screen. Now, go to the dialer and type *#197328640#
- Here, go this way:  UMTS >  Debug Screen >  Phone Control >  Network Lock > Perso SHA256 OFF > and wait for around 30 seconds. If you see at the Network Lock screen 4 options, you are good to go.
- Press on the menu button (device) and tap on Back. Then, choose  NW Lock NV Data INITIALLIZ. After about 30 seconds, you should see PERSO_NV_INIT is SUCCESSFUL. From this point , you are unlocked. You can use any sim card in the device. If you have a third carrier sim card, test it out.
- Reboot the phone and enjoy your unlocked phone. NOT SO FAST.
- Reboot back to recovery and do an advanced wipe (the following partitions: Cache, Dalvik Cache, Data and System). Restore your nandroid backup now. Don't reboot the device to system, but go and flash the MODEM and CSC. Now, you are ready to reboot back to system and enjoy your KitKat or Lollipop ROM.
Go to UMTS-COMMON-NV REBUILD and then tap Erase only Backup, then after it is done head back and tap on Make Back-up. You are all set now in case you restore the NV again by mistake, the simlock status will remain OFF.
The sim-unlocked devices do not really exist, they are just unlocked from the factory after a NV backup. If you restore the default NV, it simlocks it.
P.S. I didn't find the zip somewhere, so credits to @lamahgra for lamahgra-rom.v1.4-lite. All i did was download I9305XXALI5_I9305EVRA5_EVR.zip and extract&replace the system folder, the baseband.bin, boot.img and hidden.img and edit CSCVersion.txt and SW_Configuration.xml.