In my view these stats about UK business VoIP adoption only mean one thing.
Future growth. I say that because BT is taking a lot of steps to make VoIP more a reality throughout the UK by enabling out of market numbers which will be a boon to call centers and small business that wants to appear larger without the hassles of rate centers and mileage. They are also doing more from what my ear to the ground sources tell me overall.
Vonage has been offering all geographic numbers in the UK since it launched in 2005 so this is nothing new. In this case, BT is only offering numbers to its business customers (not residential) and for an extra £2.99/mth.