I stopped believing in polls a long time ago. They're way too easy to bias in any direction you want. A lot of it, too, is in how you ask the question. For instance, if you wanted to slant a poll in favor of Dave Barry (I don't know if he's running for president again, but he usually does), you could phrase the question something like this: "Do you feel it is more important to have a qualified candidate, such as Dave Barry, as opposed to an unqualified candidate, such as Hillary Clinton?" Some people would see through the one-sidedness of the question. Many would not.
Also, if you want a poll slanted in favor of the democrats, you could conduct your phone poll in major metropolitan areas such as Seattle or San Francisco. Sure it's random. But given the leanings of the inhabitants, you are much likely to "randomly" call someone who supports the democrats.