Hi
You can make use of class based policing to allocate 1Mbps of bandwidth to the voip traffic and 1Mbps for other applications.
You need to mark the voip traffic based on the port numbers being used by the voip traffic and then allocate the bandwidth accordingly.
Once you are done with that you can map rest of the traffic and allocated the required bandwidth to that class.
After defining the classes and relevant bandwidth apply the map onto the ethernet interface.
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/fspolic.html
For having failover on top ethernet interface u can make use of RTR feature available in the ios.
regds