I have been messing for days to get the following running.
i want to forward call when an extension is busy, but i only want this when the incoming call, is the 3rd call. So, 2 calls can be presented at all times, but number 3 and higher need to go to a different extension.
i have cooked up this sofar, but it is not working 
; wachtrij 2201
exten => 9201,1,Setvar(count9201=count9201+1)
exten => 9201,2,GotoIf(count9201>2?104:3)
exten => 9201,3,Dial(SIP/9201,175,m)
exten => 9201,4,Voicemail,u
exten => 9201,102,WaitMusicOnHold,5
exten => 9201,103,Goto,2
exten => 9201,104,Dial(SIP/9202)
exten => 9201,105,Hangup
exten => 9201,106,Setvar(count9201=count9201-1)
; wachtrij 2202
exten => 9202,1,Dial(SIP/9202,15,Ttm)
exten => 9202,2,Voicemail,u
exten => 9202,102,WaitMusicOnHold,5
exten => 9202,103,Goto,1