Yes it is. Just be sure to use it on a secure network. They went to VOIP where I used to work, within an hour of it going live I was intercepting the data, recording, and playing back to management phone conversations I got 'off the wire' using a laptop.
Yes, there's no question that VOIP is insecure. I never discuss anything sensitive on my telephone since I went with a VOIP phone. That's what encrypted email is for.