Need help agent queue

HI all,
I need HELP with asterisk
I have GSM Gateway My agents are on CellPhones is they way to make this scenario:
Agent call Asterisk and hangup to “activate” himself for queue and call forward to him
then Agent call again to “deactivate” himself
and in queue voice menu to read names of “activ” agents then user press one of numbers and call forward to that agent if hi is busy then call forward to other one ???
i think that i don’t catch a bit of asterisk jet …