Originally when I tried this out, I had the problem of not being able to find the hex string in the baseband files when using my desktop.
Eventually I got smart and moved operations to my laptop and everything showed up and worked. Not sure why it's like that.
Don't over click 'sync' otherwilse your file will be extremely huge and harder to distinguish which is the newer hex string.
Just a helpful reminder: Do NOT update your phone. By updating your software, you reset your imessage and it will revert back to using your email.
It took me several tries until I did a complete factory restore, erased all settings and such, tried it when it was a clean slate and then backed up.
It seems that you can't send the same Hex String twice to activate your phone. You'll get an "invalid input" notification.
Also, I found that you'd have to wait a few hours (not the usual 2mins) if you want to get the proper Hex string. Like last time, I just clicked the iMessage activation off and on before bed and in the morning followed the protocol.
Now it works like a dream.