From this thread you can see what this device can do. Put it on your existing plan and play no additional monthly fees. It most likely requires that you have an Android plan.

Depending on towers, you may or may not be able to get both devices running at the same time. I've personally had luck in home areas getting both to share the same data profile at the same time.

Asking $80 shipped and configured. Comes with software. These things are great in a crunch. This would be the last fee you would ever pay for it.