One of the things I'm working on at the moment is a reworked top-down forecast of the global handset industry. I.E. how many people will be spending how much for 'phones' in 5 years?
These charts illustrate why this is a pretty speculative exercise. Smartphones in general and Apple in particular added a huge amount of new revenue to the industry over the past few years, persuading large numbers of people to spend much more than they had spent in the past on phones. This process (clearest in the ASP line on the second chart) does not appear to be slowing down.