and mainly to Zuluman! for the actual fixes and modem patcher!
You can follow this solution to fix the "Emergency Calls Only" problem for those suffering from this after upgrading to 4.3 ROMS. Note this is if you have a VALID IMEI number, but are still getting Emergency Calls Only!
If you have an invalid IMEI number\Baseband problem then you need to restore a backup of your /efs folder to resolve that (follow other threads that detail how to resolve that issue)
You can safely upgrade to any 4.3 ROM now by following this solution (ORIGINAL THREAD HERE!!!)
Download the patched MK4 kernel from here:
Next download the modem (MJ9 modem patched by johnyp):
Copy these 2 files to your sdcard. Reboot to recovery and then flash the kernel then the modem and reboot, and you will no longer have the emergency calls only!
Remember this is for 4.3 ROMS only!
Note you can download the modem patcher here! This will allow you to patch modem.bin files for a modem of your choice also. Then just update the modem zip file by replacing the modem.bin with your patched modem.bin