[asterisk-users] Channel fallback

[Jaap Winius]

Hi list,

My Asterisk v1.4 system now has two ISDN channels and two SIP  
channels. The idea is to make a dialplan that mostly uses the SIP  
channels for outgoing calls, but I'd like those to fall back  
automatically to ISDN if the SIP channels aren't available, possibly  
in combination with a warning issued to the caller before the call is  
actually placed.

Is this possible with Asterisk? If so, how?

Thanks,

Jaap