based on my experience with the HD2. O2 UK just branded the software, I suppose it was because this was the first HTC phone that they had without any hadrware rebranding. I imagine it was cheaper for O2 too do it this way.
I expect the HD7 will have an O2 HUB and probably colours. In Europe O2 will be provideing 16GB storeage as opposed to the 8 GB for the unbranded European version.
I expect the phone to be SIM locked like the HD2 but you can get an unlock coade from O2. We shall see
ROM: Android NAND - MDJ Gingerbread
SPL: 2.08 HSPL