In case of Voice Over Frame-relay (VoFR) and IP/IPX on your PVCs, then you have layer2 packets which are sent in a different queue (dual-fifo queueing for vofr cisco is used) than layer 3 packets (IP and IPX). VoFR traffic takes the needed bandwidth when present and data uses the bandwidth when voice is absent in the network.
The sample config is below for one router; voice config on 3810 should not have an impact on normal data routing unless they are blocked by access-lists.
int serial 0
no ip address
encap frame-relay
frame-relay traffic-shaping
!
int serial 0.1 point-to-point
description data-pvc
ipx network 100
ip address 10.1.1.1 255.255.255.0
frame-relay interface-dlci 100
class data
!
int serial 0.2 point-to-point
description voice-pvc
no ip address
frame-relay interface-dlci 200
vofr cisco
class voice
!
map-class frame-relay data
[configs for data traffic-shaping]
!
map-class frame-relay voice
[configs for voice traffic-shaping]