As an update, we are in the testing phase of implementing guest access. We are also ensuring that guest access will be supported when using Planner within Teams!
We will update this thread again as soon as it’s available for all users.
The Planner TeamAnonymous commented
I did the same as you; added a external person to a shared One Drive area. Then I added the person to the actual plan and was able to assign tasks to that member.
I work with external users that come from both big companies as well as "one" man companies. The big companies are usually no problem regarding licens, but the small companies are more concerned about licens.
The question I have; What kind of licens must that person have? Are there any "free" licence with limited access? Or does everybody has to have the Enterprise licens?