[macro-call-callmanager]
exten => s,1,ChanIsAvail(SIP/callman02&SIP/callman01)
exten => s,2,CUT(AVAILCHAN=AVAILCHAN,,1)
exten => s,3,Dial(${AVAILCHAN}/${ARG1})
exten => s,4,Hangup


....


exten => _4XXX,1,Macro(call-callmanager,${EXTEN})
exten => 5,1,Dial(SIP/10.90.1.1/4666,10,tr)
exten => 6,1,Dial(SIP/CCM1/4675,10,tr)
exten => 7,1,Dial(SIP/callman01/4675,10,tr)
exten => 8,1,Dial(SIP/callman02/4675,10,tr)