Hi,
I have been working with Cisco VoIP since 2001 and Asterisk and freepbx ,trixbox, elastix since 2007.
I have been developing windows applications since 1996 ( VB3) and PHP since 2007.
In addition to the features you required i can also let the user login and logout of the queue etc.,
That being said I would like to have a little chat about your project to better understand the needs of the project
regards,