Follow the customer
The best part of BT is that it allows almost everything, from marketing to customer service, and it might even create a completely new service for the firm -- resulting in even more revenue. Large firms have had the capital for launching big ad campaigns on television etc, I think this is exactly why small and medium enterprises have to the most part been a bigger success story where social media is concerned, because they had a limited budget (I am assuming social media is cheaper, because social media is cheaper than television).
I think the measurement problem mentioned here is very important, linking BT with profit and revenue growth is a good start. Next maybe a large firm can compare performance of one region with BT enable with that of another region with BT not yet enabled.