search for: is_queue_member

I'm looking for a function I can put in my dial plan that tells me if a device is a member of a queue, but I can seem to find one. Basically I want to be able to dial to join a queue and if I'm already on the queue, leave...... exten => 4,1,GotoIf(${is_queue_member(queuename,SIP/${ext})}?leave:join) exten => 4,n(leave),RemoveQueueMember(queuename,SIP/${ext}) exten => 4,n,Hangup exten => 4,n(join),AddQueueMember(queuename,SIP/${ext}) or simular, If such a function exists it would be very handy.... The only way I can see of doing this is to use queue...