BT have a "Business Blog", which was news to me (I was playing about with Google's blog search to feed into a Yahoo Pipe I'm creating and it was one of the first results). Their latest post is sort of "Call For Participation" for Small/Medium Sized Business to try out some new "super top secret" product. No mention is made of what the product is, but, allegedly:
It will be of interest to businesses that spend a lot time at offsite premises - such as at those of a customer, supplier, partner or contractor - or have any of them working on your premises. And, for being good enough to help us with the trial, we'll give a free month' s subscription to the new product.
So, no real clue as to what it is. If I was to speculate, it sounds like it could be a business version of BT Fusion (where you use the offsite premise's WiFi for calls). It's the being located at a premises that makes me think it's not a pure mobile product (like some sort of product that uses 21CN's Location services would have been) and as BT Fusion doesn't appear to have a business version I would be surprised if BT wasn't working on "BT Business Fusion".