An illustrative intelligent network and method for providing voice telephony over ATM and closed user groups are provided that can provide significant advantages. A method for providing a closed user group service to authorize VToA calls includes determining the closed user group identifiers for a calling party, determining the closed user group identifiers for a called party, locating a common closed user group identifier that is common to the calling party and the called party, analyzing the privileges of the calling party in the common closed user group to determine if the calling party can make calls to other users of the common closed user group, and analyzing the privileges of the called party in the common closed user group to determine if the called party can receive calls from other users of the common closed user group. An illustrative intelligent network and data structure to provide closed user group services is also provided.