@travisg12,
Question 1. I am looking to set up a process with Microsoft Teams where we set up different extension numbers and forward each extension number externally to different phone numbers. Is this possible?
No, the Dial by extension feature is to connect with users in your organization by dialing their phone extension.
Question 2. Does each user with extension number need to have a phone system and calling plan license?
If you just want to assign an extension for user, it needs no phone system and calling plan license. If you want to use enterprise voice feature, a phone system license is necessary. About how to assign an extension to users, please refer to this article.
According to your requirement, you could add call queues to auto attendants as a workaround. Users who need to receive redirected calls could be added to call queues.
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