I have the SGH-T889 (T-Mobile USA version of the Note 2). When I got my Galaxy Note 2, I loved the device, but disliked the software. So, I decided to flash CyanogenMod 10 build from the N7100 forums. Although many things worked, the radio did not work. So, I decided (in my infinite wisdom), to
dd the radio from the Stock SGH-T889 T-Mobile rom to the /dev/block/mmcblk0p10 partition (http://forum.xda-developers.com/showthread.php?t=2039081).
This did not work, so I installed the stock SGH-T889 rom just to get it back to working order. However, my sim card was no longer being detected. I have tried flashing other roms to try and get the radio back, but alas all say that there is no sim card.
I realize I have probably permanently messed up my phone. Does anyone have any ideas or things to try to get it back to working order? I am out of things to try.
UPDATE: I have tried everything you guys have posted, and ended up sending it back to Samsung and get them to fix it under the warranty. I believe they replaced the whole motherboard, so I will never know exactly what the problem was. If you decide to send yours back, make sure to reset the binary counter that you see in download mode. There are guides around the Internet for this. Thanks for all of the help.