Hi,
I believe this scenario fits better for MQC QoS. You can tag voice traffic with DSCP EF (if not already) and put that traffic in the priority queue on the interface.
Your Routers will prioritize this voice traffic. The Internet will not.
I've seen MPLS core deployments (mainly in ISPs) using RSVP with Traffic Engineering Tunnels.
About RSVP on the Enterprise side (no MPLS) personally, I doubt there are deployments in the field out there with no MPLS cores.
Similarly, if you happen to deploy RSVP in your Routers, I don't think your ADSL/Internet line will do any reservation.
To enable RSVP, the interfaces need the command ip rsvp bandwidth.
Check the next outputs (prior and after configuring the command).
Router#show ip rsvp interface
Router#show ip rsvp installed
Router#show ip rsvp reservation
Router#show ip rsvp neighbor
Perhaps your application needs to signal the reservation by itself once you enable RSPV on the interfaces (I'm not quite sure).
HTH.
Reverences:
- Chapter: Configuring RSVP
- RSVP