Answer:
No, it doesn't mean that we can say over 50% of all people in the U.S. do not support gay marriage.
Explanation:
We are given that a telephone poll is conducted by contacting U.S. citizens via landlines about their view of gay marriage.
Suppose over 50% of those called do not support gay marriage.
Firstly, as we can see here that we have no information about the population and also how many people have been surveyed. This means that we can't say that this poll is a representative sample.
A representative sample is that which incorporates the characteristics of the whole population. As here the U.S. citizens have been contacted through landlines which means this poll does not include people who neither have landlines nor cell phones.
So, by no means, a telephone poll is a representative sample of the whole population of Us.
Hence, we can't say that over 50% of all people in the U.S. do not support gay marriage.