"Considering the source, I take it with a box of Morton's and an umbrella as well."

Seems a fitting comment when considering the future of telephone polling.  (The title of this post is a smartass remark used occasionally by Grant Lee -- real name -- a graduate school professor of mine.)

And this development is not unique to Pew Research.

Sorry, Wrong Number.   Surveying Americans by phone is increasingly problematic. As a result, pollsters are trying to incorporate new—but imperfect—alternatives.  (National Journal, 7/19/2012)

Some numbers from the article.

34%.  Cell-phone only households.  (2nd half of 2011*.)
20%.  Cell-phone only households.  (2nd half of 2008.)

60%.  Adults 25-29 in cell-phone only households.
8.5%  Adults 65+ in cell-phone only households.

*According to Chetan Sharma (paragraph 4), it's now up to 40% of households.