On April 9th, 2007 Apple announced that the 100 millionth iPod had been sold, making the iPod the fastest selling music player in history. The first iPod was sold five and a half years earlier, in November 2001.
Three months after that 100 millionth iPod, Apple sold the first iPhone.
My prediction is that sometime next year Apple will announce the 100 millionth iPhone OS device sold, making the iPhone the fastest selling platform in history. The iPhone will have been on the market for three years.
As of now there are at least 57 million iPhone/iPod touch devices in the field. This season there are likely to be over 15 million more sold. The bar to clear is therefore 28 million next year which seems achievable by Q3.
It goes without saying that 100 million contiguously addressable devices makes it the largest such device platform, but it may make it so by an order of magnitude.