Apple claims to analyze things by establishing that each new iPhone sells as much as all the other previous models together and so far their estimates proved true.
Looking at the table we find that the iPhone 3G has sold 4 times more models than the iPhone 2G, the iPhone 3Gs sold 1.6 times more devices than the first two models, iPhone 4 has sold as high as the first three versions of the iPhone and the iPhone 4S has so far scored sales totaling half those of the previous models together.
As for the iPhone 5, it is estimated that sales will be 2 times higher than those of the previous models.
Since the iPhone 4/4S will be kept on sale, it is estimated that the total number of units sold will increase adequately, but the iPhone 5 is expected to surpass them with little effort.
The site Asymco estimated that Apple will sell around 200 million iPhone 5 in 3 years and that doesn’t seem hard to achieve, given the popularity of the device.