asterisk users - Jan 2006 - PBX making ENUM lookups

Hello
I have a Siemens HiPath and I wanted to make him do ENUM lookups.
Then I connected it to an Asterisk (with ISDN) and route all calls to 
Asterisk.
Then, Asterisk does the ENUM lookup, this way:

exten=> _XXXXXXX,1,BackGround(nic.at/enum-doing)
exten=> _XXXXXXX,2,EnumLookup(351${EXTEN:})

exten=> _XXXXXXX,3,BackGround(nic.at/enum-successful)
exten=> _XXXXXXX,4,Dial(${ENUM},30,r)

But.... how do I configure Asterisk to deliver the call back to the 
Siemens PBX, if he doesnt find an ENUM match or if the contact is offline?
(I need it because its the Siemens PBX thats connected to the PSTN)

Thanks
Joao Pereira