Survey Says......

....omission of cell phone users does make a different in polling.

Pollsters: Living in a Rotary-Phone World?

Link to September 23 Pew Research Center post, "Cell Phones and the 2008 Vote: An Update".

Excerpts:
Current polling in the 2008 presidential election shows a very tight race between Democrat Barack Obama and Republican John McCain. In part because of the strong support Obama is attracting among younger voters, and as the number of Americans who are reachable only by cell phones rises, interest continues to grow in the question of whether public opinion polls that do not include cell phones are accurately measuring the relative levels of support for the two candidates.

Even though the omission of cell phones from election polls does not currently make a large difference in the substantive results, Pew's surveys this year suggest at least the possibility of a small bias in landline surveys.