In communications systems where multiple users may be associated with the same account, the voiceprint of a user is used to identify a profile of the user, facilitating identification of the user's preferences without requesting additional information from the user. The system may also monitor messages played to individual users, to control the playing of the messages to users. Calls made by users associated with the same account may be allocated to the caller initiating the call in bills, based on voiceprints. Voiceprints may be collected for use in deriving voiceprint samples during registration of a user with the system and during conversations between the user and the system. A voiceprint comparison threshold may be set based on the type of phone calling the system, to compensate for noise. Changes in phone numbers and/or addresses of users are monitored and the threshold is adjusted if changes are found.