In many Voice over IP (VoIP) systems, the end-to-end voice Quality of Service (QoS) is largely dictated by the packet loss rate and the Packet Loss Concealment (PLC) method at the receiver. Typical PLC algorithms are usually based on simple signal extrapolation methods that can produce perceptually annoying artifacts. We present a taxonomy of PLC artifacts that degrade voice quality, and demonstrate how this knowledge can be used to define a PLC-driven labeling of critical voice packets. In particular, we show how the packets whose loss will produce an annoying artifact can be labeled for transmission over a virtual premium channel effected through either a Differentiated Services method, or adaptive Forward Error Correction (FEC) on a best-effort ordinary network. With a PLC-driven labeling of critical packets transmitted over a premium channel, the VoIP application can achieve large potential QoS gains over random labeling approaches, and is more robust to packet loss over an ordinary channel. The PLC-driven labeling produces packets in bursts for the premium channel, a fact which may complicate the design of a premium channel. To automate the labeling of packets, we demonstrate the feasibility of a sender-based packet classifier to detect the packets whose loss will produce PLC artifacts.