Click to enlarge. Source: Asymco from comScore data.

FORTUNE — Drilling down into data released Friday by comScore, Asymco‘s Horace Dediu spots two interesting trends:

  • The rate at which mobile phone owners are switching from feature phones to smartphones in the U.S. has fallen off dramatically, to 300,000 per week in the three-month period ending in April from 1.5 million per week in the November survey.
  • The chief reason seems to be a slowdown in Google GOOG Android adoptions. As the chart above shows, Apple AAPL iPhone adoptions have continued to grow year over year, but Android in the April survey registered its slowest user growth since 2009. (As indicated by the height of the gray bar in the rightmost column.)

“It’s perhaps too early to suggest that we’re seeing a slowdown in the US for Android,” Dediu writes. “Perhaps there will be a return to growth in the fall. The concern has to be that rather than seeing the net adds growing — as they have for two years with only two contiguous months of decline — Android net adds have been falling for four months.”

See Trouble with the robot? for more charts and the rest of Dediu’s analysis.