The recent dip may be attributable to uncertainty over the release of windows phone 10, and also Microsoft has tended to release new phones that tend to be worse than existing phones. I delayed an upgrade waiting for a good cheap device with wp10 (Lumia 550 is not it), but got a 640 (with 8.1) when my phone had an accident.<p>WP 10 on low end phones is very laggy and horrible, which is also not good.