Yesterday I went along to the IET Appleton Lecture to hear Mike Short, R&D head for Telefonica O2.  He had some interest nuggets in his lecture: more than 50% of the World's population now have a cellphone; 85% of cellular phones are GSM.  Even the USA has 39% GSM penetration, although I suspect that is largely in the metros.  One staggering statistic is that China has 500 million cellphone users, which still leaves a huge addressable market, China has a population of 1.3 billion.