it really depends on what you mean by fully functioning BT.. I have transferred file via BT... and I have used BT to voice dial.. all on CM 6 Froyo.. which is OCd at 710 and wireless tether works... sounds great doesn't it... well wait a minute..
not all BT works.. fact is.. manufacturers have a lot of wiggle room in designing their BT devices.. if they used that wiggle room a little to much, they might work on one phone model but not another.. with Froyo, there are some models that just don't work... just like there were some that didn't work when 2.1 was released.. but they did on 1.5...