Ordered i9300 from eBay - need help to understand what's going on I've ordered a new, unlocked i9300 from eBay, and I had some adventures with it:


I've unpacked it, inserted my SIM, powered it on, and found out that the phone always thinks that I'm roaming. Instead of trying to understand what's going on, I though: "I'll just install CyanogenMod and everything will be good".
I've installed CyanogenMod 10.2 (latest stable build), only to find out that my SIM is not being detected at all. It says that Baseband is unknown, IMEI and related are unknown as well.
After trying lots of stuff, I gave up and decided to return to stock ROM (4.3). While trying to do that, I bricked my phone, and the only thing I could do is enter Odin mode.
After reading dozens of tutorials and trying lots of stuff, I ended up flushing GT-I9300_mx_20120329.pit, and that unbricked my phone.
I successfully flashed Android 4.3. This version detected my SIM, displayed the Baseband/IMEI, but it didn't connect to the cellular network. I could scan for available networks, but when I chose my network manually, it said "Selected network not available ".
I tried to flush alternative modems, but all it did is making things worse. Usually it made the phone behave like with CyanogenMod, i.e. Baseband/IMEI are unknown.
Again, after trying lots of stuff, I tried to flush Android 4.1.2. That made no change until I've stumbled on this thread. Flushing Patched_Modem_I9300XXEMG4.zip made my networking work again, and restored it to behave exactly like it did initially. Again, the phone thinks that I'm roaming all the time, but at least it works.


So currently, I have two issues:


My phone always thinks I'm roaming. Is there a fix for it?
And more important: currently, I cannot install anything other than Android 4.1.2!


Could you please shed some light on the situation? What happens with my phone? Why does it think I'm roaming? Why does the SIM work only with Patched_Modem_I9300XXEMG4? How can I make other ROMs (e.g. CyanogenMod) work?

Thanks, any help is much appreciated!
It sounds like your phone is blocked. You should try to return it if possible. If the IMEI is missing then it is very likely there is a serious problem with the radio or that it is simply blocked. You can't fix this by flashing a different ROM.