A method of providing voice services, comprising: accepting a first incoming voice call at a Private Branch Exchange, PBX, and destined for an authorizable device, to establish a voice channel for the incoming voice call, and to provide a service over the established voice channel; providing an authentication token to the authorizable device; accepting a plurality of incoming voice calls at the PBX; placing the incoming calls in a parked state; attempting to obtain call-identifying information for each accepted voice call; wherein if any accepted voice call in the parked state has call identifying information matching stored call identification information for the authorizable device, and no other accepted call has matching call identification information, and no other accepted voice call has unmatched call identification, responsive to receiving an indication, determined to be from the authorizable device, that it initiated the incoming voice call, providing the voice service over the voice channel to the authorizable device; and wherein if any of the accepted voice calls in the parked state had call-identifying information that matched the stored identification information for the authorizable device, and: there is an accepted voice call which failed to match any stored identification information or if there are more than one accepted voice calls having matching call-identifying information, then maintaining each of those incoming calls in the parked state, requesting, over data channels of devices initiating those calls, that each device send an authentication token over its voice channel, for each authentication token received, determining whether such authentication token matches the authentication token previously provided to the authorizable device, and providing the service over the voice channel from which the matching authentication token was received. accepting a first incoming voice call at a Private Branch Exchange, PBX, and destined for an authorizable device, to establish a voice channel for the incoming voice call, and to provide a service over the established voice channel; providing an authentication token to the authorizable device; accepting a plurality of incoming voice calls at the PBX; placing the incoming calls in a parked state; attempting to obtain call-identifying information for each accepted voice call; wherein if any accepted voice call in the parked state has call identifying information matching stored call identification information for the authorizable device, and no other accepted call has matching call identification information, and no other accepted voice call has unmatched call identification, responsive to receiving an indication, determined to be from the authorizable device, that it initiated the incoming voice call, providing the voice service over the voice channel to the authorizable device; and wherein if any of the accepted voice calls in the parked state had call-identifying information that matched the stored identification information for the authorizable device, and: there is an accepted voice call which failed to match any stored identification information or if there are more than one accepted voice calls having matching call-identifying information, then maintaining each of those incoming calls in the parked state, requesting, over data channels of devices initiating those calls, that each device send an authentication token over its voice channel, for each authentication token received, determining whether such authentication token matches the authentication token previously provided to the authorizable device, and if any accepted voice call in the parked state has call identifying information matching stored call identification information for the authorizable device, and no other accepted call has matching call identification information, and no other accepted voice call has unmatched call identification, responsive to receiving an indication, determined to be from the authorizable device, that it initiated the incoming voice call, providing the voice service over the voice channel to the authorizable device; and wherein if any of the accepted voice calls in the parked state had call-identifying information that matched the stored identification information for the authorizable device, and: there is an accepted voice call which failed to match any stored identification information or if there are more than one accepted voice calls having matching call-identifying information, then maintaining each of those incoming calls in the parked state, requesting, over data channels of devices initiating those calls, that each device send an authentication token over its voice channel, for each authentication token received, determining whether such authentication token matches the authentication token previously provided to the authorizable device, and providing the service over the voice channel from which the matching authentication token was received.