For a telephone survey, this consent is read to them and if they agree, they have given consent. Even if you are conducting a telephone survey, you still need to write out the consent paragraph and include it with your application. Some programs have developed or are developing blanket consent. A description of the methods by which informed consent will be obtained. A description of the method by which anonymity or confidentiality of the subjects will be maintained.
Anonymity means keeping the participants identity unknown.
Confidentiality means keeping the information provided by the participants private, available only to project staff. Sometimes you can assure confidentiality and not anonymity. It is hard to assure anonymity when you are video-taping an interview, for example. Typically, you can assure both by assigning identification numbers or asking the participants to use the last 4 digits of their social security number and keeping the raw data in a locked file box. Because of some recent changes in the Freedom of Information Act, it is recommended that if the list of identification numbers is linked to names, that that list be kept separate from the raw data.