Does magic jack work on Ubuntu?

It does not work out of the box. Apparently magic jack itself was developing linux drivers but they terminated the project. there are some ways to get it to work though.

If you connect your magic jack with your router you can use it with the guide at the bottom of this page

If you connect your magic jack with your pc you will need to run it with a virtual machine You can use this guide

I hope this helps

It does seem that someone has managed to get MagicJack working in Linux, at least, as of 2010. Beware, however, as it appears this solution is rather technical and may void your warranty and/or violate your terms of service.

It may also be possible to get it working using your router with MagicJack Plus.

MagicJack said they were going to support Linux in September 2011, but as of June 2013, they still don't.

I'd personally recommend going with MagicJack Plus and trying to get it working with your router.