I apologize for the mis-information @bigjay1114
I have successfully recovered mine, but before you flash these files, I must ask, did you perform a backup? If so, this will be simple. If not, you might want to just stay with the T599UVAMD5 setup... it's not going to hurt... because on a positive note, we have found another baseband that is compatible with the SGH-T599N!
IF YOU DID NOT BACK UP YOUR PHONE BEFORE YOU FLASHED, DO NOT ATTEMPT THE FOLLOWING
Same steps as before...
Go to your terminal in TWRP Advanced menu, make sure you're on top-level.
If your files are on the INTERNAL storage, then type these....
dd if=/sdcard/modem.bin of=/dev/block/mmcblk0p16
dd if=/sdcard/modem.img of=/dev/block/mmcblk0p12
If your files are on your SD-Card, then type these...
dd if=/external_sd/modem.bin of=/dev/block/mmcblk0p16
dd if=/external_sd/modem.img of=/dev/block/mmcblk0p12
Reboot. You will not have service. This is where your backup comes in to play.
Reboot into recovery again, and restore your phone. Once done, you should have service again, and back on the stock baseband, T599NUVAMD4.
, I sincerely apologize for the mixup.
To anyone who has flashed these files, please contact me if you are having issues with loss of signal AFTER recovering to the original files, and I will walk you through any additional steps that I can find.