I'm blogging from an airport with just enough time to like and block quote two helpful explanations of what the missing "cell phone only" households mean to the vast majority of surveys that do not attempt to interview Americans on their cell phones.
First, Wall Street Journal "Numbers Guy" Carl Bialik has a very clear, concise review of the central issues. He draws on conversations with both Jeff Jones of Gallup and Scott Keeter of the Pew Research Center, the two organizations that have done the most significant political surveys of Americans over their cell phones. It is well worth reading in full if you are new to this issue. Bialik stresses that the evidence so far shows that the missing "cell onlys" have little impact on political survey results:
The impact of losing cellphone-only respondents, however, may be exaggerated. Their numbers aren't big enough to budge most poll results by more than a point or two, Gallup has found.
People who use only cellphones, on average, are younger, more likely to rent their homes and have lower incomes than their tethered-telephone peers. But once you adjust for age, cellphone-only users have similar political viewpoints. Although he thinks cellphones should be included, Jeffrey M. Jones, managing editor of the Gallup Poll, asks, "It's still a lot of cost and effort, and what's the payoff?"
Meanwhile the Pew Research Center yesterday released another mega-study of the cell-phone-only issue. It's a must read for those who want all the nitty-gritty details. Here's the bottom line:
On key political measures such as presidential approval, Iraq policy, presidential primary voter preference, and party affiliation, respondents reached on cell phones hold attitudes that are very similar to those reached on landline telephones. Analysis of two separate nationwide studies shows that including interviews conducted by cell phone does not substantially change any key survey findings.
Update: Carl Bialik has much more on his blog, and also reminds me to link to the recent Public Opinion Quarterly special issue on cell phone surveys and my own series from last summer on the cell phones and political surveys (Part I and Part II).