Lots of confusion on this thread. SIP never handles actual voice traffic. It is just a signaling protocol used to initiate the ICE process of actually establish

Lots of confusion on this thread. SIP never handles actual voice traffic. It is just a signaling protocol used to initiate the ICE process of actually establishing the connection, either a direct p2p connection or a relayed connection using TURN when the NATs can't be traversed. That's when traffic is typically UDP, as it's easier to traverse NATs with UDP. The transport SIP uses is largely irrelevant, although it's pretty silly for it to use anything but TCP because reliability of sending the offer and the answer is pretty important, and they can be sent in multiple packets.