Does it make any sense it terms of perfomance and latency?As far as i know TOR is a transports layer protocol trying to encapsulate the cells with onion routing in order to enhanse privacy.Since sip is widely used as a session protocol for voip calls what do you believe about perfomances of that incarnation?
Remember that just using TOR for SIP (and not for actual data) isn't good for anonymizing your connection.
Using voip over TOR is definitely foolish, because TOR is slow by it's nature. Your traffic will go through multiple nodes, some being normal home broadband connections. Each connection adds latency, in my experience with rather much (latencies over 200ms are more than common, and it's not my end).
Performance (bandwidth) really depends on your luck. You may get fast connection, or may not. And it also changes regularly, so fast connection may change to horribly slow. Remember that your connection is as slow as slowest link between you and exit node.