In iax.conf:
[fiery]
type            = user
context         = fiery-enum-incoming
accountcode     = enumuser

In enum.conf:
[general]
search => enum.fierymoon.com

In extensions.conf:
[fiery-enum-incoming]
exten => _17804254798,1,Goto(${MAIN_CONTEXT},${MAIN_EXTEN},1)    ; Incoming call for us via ENUM
exten => _1NXXNXXXXXX,1,SetVar(enumok=0)
exten => _1NXXNXXXXXX,2,DBget(enumok=enumok/${EXTEN:1:6})
exten => _1NXXNXXXXXX,3,GotoIf(${enumok}?4:900)
exten => _1NXXNXXXXXX,4,ChanIsAvail(Zap/1)
exten => _1NXXNXXXXXX,5,Dial(Zap/1/${EXTEN:4})
exten => _1NXXNXXXXXX,6,Hangup
exten => _1NXXNXXXXXX,105,Playtones(busy)
exten => _1NXXNXXXXXX,106,Wait(10)
exten => _1NXXNXXXXXX,107,Hangup
exten => _1NXXNXXXXXX,900,Congestion