Visual exploration of massive data sets arising in the telecommunication industry is a challenge. This paper describes a number of different techniques for visually exploring large data sets. The techniques cover a wide range of techniques, including statistical 2D displays, pixel-oriented displays, and dynamic 3D displays with variable resolution. The techniques have been successfully applied in the telecommunications industry to analyze call detail data for understanding customer behavior and preventing fraudulent usage, and to monitor network traffic for analyzing unexpected network events such as high volumes of unanswered calls.