Be wary of surveys

Most surveys of national elections are based on telephone calls. In 1936 the major national survey by the Literary Digest predicted that Alf Landon would handily defeat Franklin Roosevelt. It was quite wrong. Why? Because it was a survey of people who had telephones and eliminated most of the lower class that did not have phones. A friend of mine wonders if a similar condition exists today in the day of the cell phone. Many, many people have only cell phones, for which there is no central directory. So, in 1936 the survey was flawed because of the lack of phones. But, in 2016 will it be flawed because of too many phones?