asterisk users - Apr 2006 - Querying number of people in a call queue from dialplan

Is there any way to query the number of people in a call queue from the
dialplan?

Our freephone provider has a feature where if we busy a call they record
the voicemail and email it to us. This enables us to divert calls to
them if our incoming lines start to get full. In order to do this we
need to decide whether to busy the call before passing it into the
queue.

Thanks
Gareth