All projections to do with IoT have been in 'telephone numbers'. Variously, analysts have projected numbers of connected IoT devices growing to as few as 30 billion, and as many as 75 billion devices world-wide by 2020. 

In the past I have generally found analysts tend to overestimate emerging market sizes.  But it all becomes very real when you see €11b of cellular telecoms revenue in the last calendar year driven off the back of the IoT roll-out.