Question : Problem: CISCO Router VPN for Multiple Internet Providers

I have a current client with 2 Dedicated Internet Access T1's at each locations with a VPN tunnel to connect to each other.

I would like to setup redundancy via a WISP provider which hands ethernet.

The question is can a VPN be setup for a Virtual Interface (ie: Loopback IP Address)?  The Serial interface has a public IP address & the Ethernet interface will have a public IP address. How can I configure the VPN so that if one interface goes down the redundant interface will pass VPN traffic without manaully changing the config?

Answer : Problem: CISCO Router VPN for Multiple Internet Providers

Here's a config example for DMVPN
http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a0080455c71.html

It might be over complicating matters rather than just using the secondary peer config in the IPSEC. I would start with that. The new features of 12.3 forward with respect to Dead Peer Detection makes this a much more viable alternative.
http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_white_paper09186a00801ee19a.shtml