Telemarketing improves quality control. Experienced and professional telemarketers will administer the telephone surveys. They will guide your respondents to answer and interpret questions correctly.
Telemarketing increases response rate. How? There are several telephone surveys already conducted using the telephone that are able to yield better response rate than web or mail. I think the best reason for this is that people are more comfortable answering surveys in verbal than in written.
Telemarketing is a more direct approach. Telephone surveys give your campaign a personal touch. Live people can make your respondents more open and forthcoming with their answers.
Telemarketing promotes openness and trust. The fact that there is some level of anonymity over the phone, phone surveys motivate respondents to be more honest and comfortable with their responses.
Market research is an indispensable aspect of your business. It will save you big bucks from producing products/services that are not marketable to your target audience. Yes, there are several more strategies out there that you can use to conduct a study about your market, but if you are considering the speed and cost of doing it, telemarketing is the best choice.