Once a voice signal is packetized, its just like any other traffic (data, video etc). So pretty much any router can route that traffic. The question is what type of qos techniques can be deployed on the router in question to honor voice traffic.
For a router like 1841, which doesnt natively support voice terminations on the box, but can still route packetized voice, it supports MQC (modular qos cli) and qos packet marking with IP base image.
Sankar
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Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus