A method and system are disclosed for providing voice communication over a packetized network in which quality of service is guaranteed for voice communications. The method involves identifying reserved paths within the network, such as multi-protocol label switching paths. When a call is made, the identified reserved paths are evaluated to determine whether each contains sufficient bandwidth for the requested voice communication. The effective bandwidth for the call is estimated based on the codec used for the call, the service class parameter set from the caller's user profile, the time of day, and other parameters. A priority parameter is set for the requested voice communication, which may be based on the service class parameter, and is mapped to a specific Differentiated Service Code Point (DSCP) and 802.1p service class parameter. If the reserved path is determined to contain sufficient bandwidth, the requested voice communication is transmitted over the reserved path at the set priority. If the path does not contain sufficient bandwidth, an error message is sent to inform the caller that QoS can not be guaranteed for the call, and a decision is made whether the call should proceed nevertheless.