Don't know if this is any help to you but...
I have an N80 on three, and got an interesting response from my local Nokia Service Centre when I phoned them up for a firmware update. Basically, I want(ed) to run the Navicore sat-nav stuff on my phone, and the Navicore site was stating that I would need a higher firmware version than I possessed.
So, I phone my local NSC, who are gung-ho to do the update, until I mention that the phone is on three. I then get a different story altogether. According to the man on the phone, as well as being a three specific version of firmware (no surprise there), he said that it was not possible to map version numbers of three firmware against generic version numbers. He said that I would need to being the phone in and then they could connect it up, and off it would go across the interwebbe to Nokias machinery which would then tell them the *real* firmware number.
-- End of that episode --
Next, I email Nokia about this issue, and, as yet, after going on for 2 weeks, no response.
-- End of that episode --
Next, I email three, and ask them the same. I get called a couple of days ago by a guy who was keen to resolve my issue. I explained my problem, in that I was hardly going to go out and buy some softare for the phone if there was no guarantee it would run on my firmware level. So, his response was that I could flash the phone with the generic version, and they would send me text messages to restore three specific settings. I then asked him to confirm that this was OK to do, in terms of usage with three etc, and he went off and did some more poking around, came back, and informed he that "it was not recommended" to use generic firmware, but it would not be a problem with then, and they would happily send me the text messages for restoring settings.
As yet, I have done nothing about this, but I am tempted to 'go generic'. I guess you could do the same, if you just go to a NSC, rather than OTA updates.
Don't know if this helps, but...