I have BIS - Orange business
UMA seems to work.
I moved from an o2 8900 to an Orange 8900 JUST to get UMA.
I live in a patchy phone reception area in London and when EDGE and GPRS both disappear UMA pops up to the rescue..
Not very nice quality but seems to work..
I don't thinks its got all the sophistication of USA UMA - I wouldn't trust it to 'seamlessly' hop over from UMA to GPRS / EDGE as I walk or drive away from my house. (I need to test that!) But perhaps it will come in handy on trips abroad.. One can only hope - and THAT what I want it for - I am sick of getting killed on outside UK work trip phone bills
No one knows anything about UMA in the UK - especially not the network operators!
As for the billing - on these forums those speculations lead to epic arguments and contradicting opinion.. I think it is NETWORK dependent - so its no use a German or US based person trying to tell you... But
good luck finding someone that works for Orange UK that actually KNOWS the answer....
You might just have to wait and see how your monthly bills come out to really find out for sure..
Post your news on it here and good luck..