I had CM7.1 installed and, as you know, you cannot activate service on an ASOP rom.
I tried a few 'stock root' roms that I found in the development forum, but none of them would allow the ## code: ##72786#. (Carrier reset).
They would simply freeze once this was entered and not allow you to continue.
Eventually I tried Supreme Sense v-XII, and this allowed the Carrier reset ## code to work and activation to occur.
So if anyone has this problem in the future, you might give Supreme Sense v-XII a try.