I think it would be very interesting if polling orgs. would list the number of calls they had to make in order to get whatever benchmark they end up using.
I don't know if the statistic is valid, but I read a report that sid the pollsters get about a 10% response rate. Call 10 numbers to get one person to take the poll. I figure some of those calls are ring-no-answer, others are hangups, maybe some people start and hang up because it is taking too long.