Abstract: A small, wireless, battery operated monitoring apparatus is provided that is installed by a user on a cellular telephone in close proximity to a telephone antenna. The monitoring device monitors telephone usage by detecting and tracking radio frequency signal transmissions from the antenna to a base station. The monitoring device includes a microprocessor that performs functions on data indicative of cellular telephone usage and the customer billing plan. The microprocessor, under control of a call processing program, determines exactly when cellular mobile service is established and terminated at the cellular telephone. Under control of a time tracking program, the microprocessor monitors telephone usage, and generates statistical information indicative of telephone usage. The tracking program allows the user to set parameter values associated with statistical information indicative of a customer billing plan and the current date and time.