[Asterisk-Users] Backup POTS line

[Remco Barende]

I have two * servers that are connected with IAX2. Each server has one 
pots line attached to it, the users connected to it can dial out by 
dialing a 9 and then the telephone number. So far nothing spectacular.

Is it possible however to use the remote POTS line if the local POTS line 
is in use? (sort of fail-over?).

Ideally I would like two solutions to this:
1. transparent to the user, just use the other line
2. purposely chose the other line by dialing 8 for example

Is this possible? I have this in my extensions.conf for the local POTS 
line.

[pots-out]
exten => _9.,1,Dial(ZAP/g1/${EXTEN:1},70,T)
exten => _1NXXNXXXXXX,1,Dial(ZAP/g1/${EXTEN})
exten => _NXXXXXX,1,Dial(ZAP/g1/${EXTEN})
exten => _9.,2,Macro(fastbusy)
exten => _9.,102,Macro(fastbusy)

Thanks!!