Coverage bias: A telephone survey suffer from coverage bias because it cannot include viewers without telephones.
Voluntary response bias: Voluntary response bias occurs when sample members are self-selected volunteers. The persons who have a strong opinion (who feel strongly that they should answer the question) is likely to call. The resulting sample tends to overrepresent individuals who have strong opinions.
(ii) Apart from the biases stated above, the resulting opinion can not be taken as "public opinion" since the number of people who call there is a very small part of the total population.
(b)-- Try yourself.