Briley, Bruce E.
Introduction to telephone switching / Bruce E. Briley
Addison-Wesley, Advanced Book Program , 1983
 Buku Teks
Kleinau, Karl-Heinz
Telephone installation / Karl-Heinz Kleinau
Edition Leipzig, 1965
 Buku Teks
Goldner, Paul S.
Red hot cold call selling
American Management Association;, 2006
 eBooks
Boyan, Lee
Successful cold call selling
American Management Association, 1989
 eBooks
Frey, James H.
Survey research by telephone
Sage Publications, 1983
 Buku Referensi