@book{Call1993,
  author    = {Call, Guido},
  title     = {H{\"o}rfunkstudie 1993 - Die Programmakzeptanz des Belgischen Rundfunks in der Euregio},
  address   = {Aachen},
  year      = {1993},
  language  = {de}
}
@book{Call2008,
  author    = {Call, Guido},
  title     = {Kunden- und Servicemanagement : erfolgreich der Servicew{\"u}ste entgehen},
  publisher = {Kovac},
  address   = {Hamburg},
  isbn      = {978-3-8300-3890-0},
  pages     = {147 S. : Ill., graph. Darst.},
  year      = {2008},
  language  = {de}
}