However, I have made an interesting discovert. My IMEI is still on the phone. I know this because I have twice managed to connect to the network after many reboots and my IMEI was read correctly in the log file when I reset back to stock.
I decided to root my phone (I have since unrooted) and found that the EFS files m9kefs1, m9kefs2 and m9kefs3 are all 0 bytes. So are all the other files in the folder. I even have backups of these files, and the file sizes update when I copy them in, but when I reboot the phone resets the file sizes back to 0 bytes.
Why is this happening?
On a side note, resetting your phone to stock doesn't actually seem to do anything as you are still required to do a factory reset. Surely all of the files should be deleted?