According to a document published by IDC, the Worldwide Hotspot Forcast, hotspot users will number nearly 25 million by 2008.
From the publication:
Over the next five years, IDC expects the hotspot market to evolve through two distinct phases – two years of massive network footprint expansion followed by three years of intense relationship building among carriers, network operators, and service providers. The first phase will be characterized by dramatic growth in both the number of hotspots and hotspot users. Over the next five years, IDC projects the worldwide number of available commercial hotspots will increase at a compound annual growth rate (CAGR) of nearly 57% while the number of worldwide hotspot users will approach 25 million.