A method of estimating the quality of speech information associated with a voice call over a communication system comprising a core network and an access network where speech information is carried between the access network and the core network and within the core network in frames. The method comprises determining a rate of frame loss for frames transported between the access network and the core network and/or within the core network, and mapping the rate of frame loss to a quality estimation value using data collected by simulating frame loss on representative speech samples and determining quality estimation values for the damaged speech samples.