Now that Microsoft Teams is generally available, I wanted to provide a video demo showing how you can import an existing Plan into Teams.
Here are the steps and important items to not...
Updated Mar 28, 2017
Version 2.0
Blog Post
Sam Nicolitsi I was confused by the process of merging a team with an O365 Group at first. I replied to your post earlier with details but somehow it was deleted.
To keep it short here is the key. When creating a Team to associate with an O365 Group you must not create a new Team. After selecting Create Team you will see something towards the bottom of the screen that says.
Add Microsoft Teams to an existing Office O365 group. It does not look like you can click on it but you can. Do NOT enter a new name in the Team Name field. Then any O365 Group that you are the admin for will be listed with radio buttons. If you are not the admin of the group you want to merge it will not work.
Do not put a new Team name in or it will create a Team that is not associated with the group.