The latest data from comScore MobiLens is showing an uncharacteristic slowing in smartphone growth. In the survey period ending November, the number of smartphone users in the US was 91.4 million. This is equivalent to 39.1% penetration, an increase of 0.6% (i.e. up from 38.5% in the last period.)
The growth is equivalent to 1.4 million new smartphone users (i.e. users who switched from a non-smart device for the first time.) The problem is that this is half the growth of the previous period.
Horace Dediu identifies an unprecedented slowdown of Android growth in comScore’s November survey results. While he doesn’t offer any theories as to why, there is some interesting discussion on this topic in the comments.