Sumber buku  :

1. John E Kennedy, R. Dermawan Soemanagar. 2006. Market Communication. Jakarta. Penerbit Bhuana

    Ilmu Populer.

2. Robert W. Bly. 1997. Secrets of Successful Telephone Selling. Penerbit Henry Holt and Company.

3. David Salmon. 2016. 20 Top Telephone Sales Tips. E - book