Cisco Router Dual WAN failover


I am in need of some assistance on configuring a Cisco router (1721, or 1841, or 2800) with Dual WAN and failover with route maps. Let me give some backround of the setup.

We have a Cisco 1721 router with a point to point T1 and a Comcast Cable connection with 5 static IP's.

We use the T1 for both voice and data with failover to the Comcast cable if the T1 were to fail. That setup works great but we get very minimal bandwidth on that T1 and would like to use the Comcast cable for data bandwidth while keeping the voice over the T1. We would also like these connections to failover to one another in the event one were to fail.

That being said. Both connections will be plugged into the same router The T1 in a CSU and the Comcast in an Ethernet WIC. I assume there are route maps involved for each VLAN (voice and data) but not sure how to route data traffic over the comcast without 2 public IP blocks from the comcast side.

Can anyone help?
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Do you use VoIP on the T1 circuit or is it a fractional T1 with pri voice and data on the same t-1. If you use VoIP on the T1 you can use ip sla to control static route entries to the ITSP over the T1 and if its down use the Comcast connection and vice versa for data
Sample config
ip sla monitor 1
 ! Replace Loopback 10 with interface Comcast internet is connected
 type echo protocol ipIcmpEcho source-interface loopback 10
 timeout 2000
 frequency 2
track 1 ip sla 1
ip sla monitor schedule 1 start-time now lifetime forever
!SLA for T-1
ip sla monitor 2
 ! Replace Loopback 20 with interface T-1 internet is connected
 type echo protocol ipIcmpEcho source-interface loopback 20
 timeout 2000
 frequency 2
track 2 ip sla 2
ip sla monitor schedule 2 start-time now lifetime forever
!Chenge subnet to ITSP subnet
ip route interface loopback 20 10 track 2
ip route interface loopback 10 30  track 1
ip route interface loopback 10 10 track 1
ip route interface loopback 10 20 track 2

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