A procedure for measuring the frequency shift and phase jitter of telephone data channels in the voice frequency band (300-3400 Hz) is presented. Rather than processing a received signal to obtain the required measurements, the phase is extracted and processed by a ‘phase filter’. An implementation of the phase filter is described which utilises power-2 coefficients to avoid the need for multiplication. This procedure is based on modern signal processing techniques which allow both simple and fast operation when implemented using a microprocessor. The technique can thus be easily incorporated into a telephone line measuring equipment or communication network monitoring system. Simulation results are given showing the effect of noise on the accuracy of the proposed algorithm, and some methods for the reduction of noise are also described. The trade-offs between the test signal duration and measurement accuracy are also considered.