Question [Q] Unlock a SIM locked Xperia M

So my gf got an Orange Xperia M and would like to use a O2 SIM in it. It's obviously locked to Orange so right now it's asking for an unlock code when the O2 sim is installed.

I checked the service menu and her bootloader is locked tight too:

bootloader unlock allowed: No

I read that you need to unlock fastboot for the Sim lock to drop. Any way to do that?
We don't really need to unlock the bootloader at this stage just the sim lock.

Thanks a bunch.