dialplan:

[testing]

exten => _000.,1,Set(GROUP()=INBOUND@QueueCall)
exten => _000.,n,Set(ODBC_CREATECOUNT()=${GROUP_MATCH_COUNT(.*@INBOUND)}\,${GROUP_MATCH_COUNT(.*@OUTBOUND)}\,[none]\,0)
exten => _000.,n,Verbose(INBOUND TEST ANSWER ${EXTEN} CAUSE NORMAL)
exten => _000.,n,Ringing()
exten => _000.,n,Set(RINGTIME=${RAND(3,9)})
exten => _000.,n,Set(CALLTIME=${RAND(30,45)})
exten => _000.,n,Wait(${RINGTIME})
exten => _000.,n,Set(TIMEOUT(absolute)=${CALLTIME})
exten => _000.,n,Answer()
exten => _000.,n,MusicOnHold()
exten => _000.,n,Hangup()

exten => _001.,1,Set(GROUP()=INBOUND@QueueCall)
exten => _001.,n,Set(ODBC_CREATECOUNT()=${GROUP_MATCH_COUNT(.*@INBOUND)}\,${GROUP_MATCH_COUNT(.*@OUTBOUND)}\,[none]\,0)
exten => _001.,n,Verbose(INBOUND TEST NO ANSWER ${EXTEN} CAUSE 19)
exten => _001.,n,Ringing()
exten => _001.,n,Set(RINGTIME=${RAND(3,5)})
exten => _001.,n,Wait(${RINGTIME})
exten => _001.,n,Set(PRI_CAUSE=19)
exten => _001.,n,Hangup()

exten => _002.,1,Set(GROUP()=INBOUND@QueueCall)
exten => _002.,n,Set(ODBC_CREATECOUNT()=${GROUP_MATCH_COUNT(.*@INBOUND)}\,${GROUP_MATCH_COUNT(.*@OUTBOUND)}\,[none]\,0)
exten => _002.,n,Verbose(INBOUND TEST BAD NUMBER ${EXTEN} CAUSE 21)
exten => _002.,n,Set(PRI_CAUSE=21)
exten => _002.,n,Hangup()

exten => _003.,1,Set(GROUP()=INBOUND@QueueCall)
exten => _003.,n,Set(ODBC_CREATECOUNT()=${GROUP_MATCH_COUNT(.*@INBOUND)}\,${GROUP_MATCH_COUNT(.*@OUTBOUND)}\,[none]\,0)
exten => _003.,n,Verbose(INBOUND TEST BUSY NUMBER ${EXTEN} CAUSE 17)
exten => _003.,n,Set(PRI_CAUSE=17)
exten => _003.,n,Hangup()

exten => h,1,Verbose(INBOUND HANGUP)

[DialExternal]

exten => _X.,1,Dial(Zap/g3/${EXTEN},120)
exten => _X.,n,Hangup()

exten => h,1,Verbose(DialExternal ${CHANNEL} ${STRFTIME(||%m/%d/%Y %T.000)} HANGUP [${DIALSTATUS}/${HANGUPCAUSE}])

============================================================================================================
Dialling 0000:
INBOUND TEST ANSWER 0000 CAUSE NORMAL
DialExternal SIP/5711-08bba230 09/25/2007 19:36:08.000 HANGUP [ANSWER/16]
INBOUND HANGUP

[All seems ok]

Dialling 0011:
INBOUND TEST NO ANSWER 0011 CAUSE 19
INBOUND HANGUP
[Sep 25 19:36:20] WARNING[16698]: app_dial.c:741 wait_for_answer: Unable to forward voice or dtmf
DialExternal SIP/5711-08bba230 09/25/2007 19:36:20.000 HANGUP [CHANUNAVAIL/19]

[Why CHANUNAVAIL ? Q931 gives 19 as AST_CAUSE_NO_ANSWER]


Dialling 0022:
INBOUND TEST BAD NUMBER 0022 CAUSE 21
INBOUND HANGUP
DialExternal SIP/5711-08b3c2c0 09/25/2007 19:36:34.000 HANGUP [CONGESTION/21]

[Why CONGESTION ? Q931 gives 21 as AST_CAUSE_CALL_REJECTED, AST_CAUSE_NORMAL_CIRCUIT_CONGESTION IS 34] 

Dialling 0033:
INBOUND TEST BUSY NUMBER 0033 CAUSE 17
INBOUND HANGUP
DialExternal SIP/5711-08b14fd0 09/25/2007 19:36:41.000 HANGUP [BUSY/17]

[All Seems Ok]
===============================================================================================================