I prefer to use floating statics. I have an ISDN BRI available at each site, and a PRI interface at the central site. I have a static default route from the remote site to the central site via the T1 line (or in my case the E1 line). I then have a dialer profile from the remote site to the central, using the BRI ISDN connection. I make another default route from the remote site to the central via the dialer profile, but with a high administrative distance, say 240. This way, the route via the ISDN does not get dialled until the main serial line goes down. If server traffic is a problem on the ISDN line, I can apply traffic shaping to give my management traffic priority.
The floating static scheme works even if you are using a routing protocol, and even if you cannot detect the line down directly; just make sure that the administrative distance of the floating static is greater than that of your routing protocol.
http://www.cisco.com/en/US/tech/tk801/tk133/technologies_configuration_example09186a0080093f7e.shtml
http://www.cisco.com/en/US/tech/tk713/tk237/technologies_configuration_example09186a00800a3b77.shtml
Alternatively, you could just use the backup command to trigger you dialup link:
http://www.cisco.com/en/US/tech/tk801/tk133/technologies_configuration_example09186a008009455d.shtml
Kevin Dorrell
Luxembourg