ISDN backup with two default groups

[Normskin]

I have a router that uses ISDN as a backup method. Currently it also has a defalut route pointing towards their firewall, however, in the event of a route from their hub site going down, dialer watch forms a connection using ISDN. The thing is, I wanted to use another default route to point all traffic coming from this spoke site to the ISDN connection. How will these two default routes work ?

Any problem I haven't seen?

ip route 0.0.0.0 0.0.0.0 206.182.96.2 => Firewall at site
ip route 0.0.0.0 0.0.0.0 172.17.34.34 250 => ISDN to hub.

The weighted route is the ISDN connection.

Norman.