1. A voice messaging system for converting an audio message from a caller into text, the voice messaging system comprising: at least one automatic speech recognition (ASR) system to automatically recognize at least some of the audio message; a computer implemented preprocessing front-end to process the audio message from the caller and to detect if the audio message contains no voice content, wherein: if the preprocessing front-end detects that the audio message contains no voice content, the preprocessing front-end does not provide the audio message to the ASR component; and if the preprocessing front-end detects that the audio message contains voice content, the front-end provides the audio message to the ASR component, and wherein the computer implemented preprocessing front-end comprises a computer implemented speech quality detector to determine at least one measure of speech quality of the voice content of the audio message, and wherein the speech quality detector detects drop-outs, estimates noise levels and/or calculates an overall measure of voice quality using an adaptive threshold to reject lowest quality messages.