This document describes research into developing non-intrusive models for estimating voice over IP (VoIP) call quality using genetic programming. The researchers created a VoIP simulation environment and used it to generate training data representing different network conditions. Genetic programming experiments were performed to evolve models relating network parameters like packet loss to MOS scores. The best models achieved good accuracy compared to intrusive quality estimation methods, using only 1-3 variables. The models allow real-time VoIP quality monitoring without a reference signal.