It believes the market for expensive smartphones is just about tapped out and therefore Apple's growth is going to be held in check.
In this chart, you can see that Pacific Crest believes growth is going to stall in the next two years as upgrades quickly become the bulk of iPhone purchases instead of sales to new users.
If there is one legitimate case to be made against Apple's growth, this is it. Can Apple continue to sell iPhones, which are $650 each, to new users?
Source : Business Insider SAI January 2013