The "Personal" plan fits for users who want to activate the feature for their accounts only and they are charged only for one user. You can subscribe at a personal account (Sign-In).
The "Team" plan makes voice messages available for all users in the Slack workspace (for current and new).
We charge a fixed price for Slack workspace per month (not per each user). Only the user responsible for your team pays. Usually, this user is the manager of the team.