Thanks el_es,
I will have to look into your suggestion, but previously when I've used queues I've found that the queue answers the in coming call which is not what I need it to do.
The reason that i don't want the call answered straight away is because the PSTN gateway is in a remote location and there is also an analogue phone plugged in to the same PSTN line which they might want to answer, but if the situation occurs that no extensions are registered the call will get answered straight way by the pbx with the 'number is not in service' message which is what I want to avoid.
Peter.