A system to perform textual queries on voice communications, the system comprising: an index service for storing a plurality of audio content data sets for a plurality of voice communications, the plurality of audio content data sets comprising at least two audio content data sets for each voice communication, the at least two audio content data sets being selected from a speech-to-text audio content data set generated using a speech-to-text conversion technique, a phoneme audio content data set generated using a phoneme lattice technique, and a keyword audio content data set generated using a keyword identification technique; and a search engine configured to: receive search criteria from a user, the search criteria comprising at least one keyword; search each of the at least two audio content data sets for at least a portion of the plurality of voice communications to identify voice communications matching the search criteria; and combine the voice communications identified by each search to produce a combined list of identified voice communications, said system being characterized in that combining the voice communications identified by each search comprises: assigning each identified voice communication a match score based on a comparison of the voice communication and the search criteria; and generating for each identified voice communication a weighted sum of the match scores for the voice communication, the weight of each match score being based on the particular audio content data set that identified the voice communication. an index service for storing a plurality of audio content data sets for a plurality of voice communications, the plurality of audio content data sets comprising at least two audio content data sets for each voice communication, the at least two audio content data sets being selected from a speech-to-text audio content data set generated using a speech-to-text conversion technique, a phoneme audio content data set generated using a phoneme lattice technique, and a keyword audio content data set generated using a keyword identification technique; and a search engine configured to: receive search criteria from a user, the search criteria comprising at least one keyword; search each of the at least two audio content data sets for at least a portion of the plurality of voice communications to identify voice communications matching the search criteria; and combine the voice communications identified by each search to produce a combined list of identified voice communications, receive search criteria from a user, the search criteria comprising at least one keyword; search each of the at least two audio content data sets for at least a portion of the plurality of voice communications to identify voice communications matching the search criteria; and combine the voice communications identified by each search to produce a combined list of identified voice communications, said system being characterized in that combining the voice communications identified by each search comprises: assigning each identified voice communication a match score based on a comparison of the voice communication and the search criteria; and generating for each identified voice communication a weighted sum of the match scores for the voice communication, the weight of each match score being based on the particular audio content data set that identified the voice communication. assigning each identified voice communication a match score based on a comparison of the voice communication and the search criteria; and generating for each identified voice communication a weighted sum of the match scores for the voice communication, the weight of each match score being based on the particular audio content data set that identified the voice communication.