A KIV 19 appears to be just an encryption device. Provided your network has routes to whom you intend on calling, a SX20 or any codec would be able to make a call. The SX20 is unaware of the KIV 19 and the KIV 19 is unaware of the SX20. I would potentially back off the MTU on your codec seeing how your networking traffic passing through the KIV 19 would have a larger then normal 1500 transfer unit. I hope that helps.