"There is growing concern within the polling business about how long
the landline telephone survey will remain a viable data collection
tool" because of the cell-phone only population not being
counted. ... Pew estimates that interviewing a cell-only respondent
costs approximately four to five times as much as a landline respondent."
http://pewresearch.org/pubs/515/polling-cell-only-problem
www.peoplewho.org