Sky Fibre only started in April, so they could have started shipping the 2504n then with dual mode firmware.
I got a 2504n in June (old router was playing up) and then another in August when i got fibre. Seems a bit of a waste.
2nd option - sky can do firmware upgrades automatically - why couldn't my firmware be updated remotely to support fibre?
Sky Fibre Unlimited
Ashington (Northumberland) Exchange