[vox-tech] Using dial-up as backup for DSL

[Paul]

Since my DSL was down for about 4hrs today (thanks pacbell/sbc/att) I'm 
trying to figure out how to setup my server box and a modem as a 
fallback when my dsl line goes down.
I remember, pre dsl, I used diald with a modem on a second phone line 
but that was "hardwired" into the configuration.
I think what I need now is a relatively easy way to switch my Internet 
connection between my firewall/nat/router and my server box.
I know somebody out there has the same problem and has a web page 
explaining how to do it, but all I can find are pages on how to setup 
dsl or ppp, not both.
Any thoughts, ideas, urls ...
Am I even asking the right question?
Thanks
Paul