Does voice calling require a subscription?

I’m working on a proof of concept of voice-only calling integration into our web app. My tests are going well so far, but I was wondering how exactly billing works in this scenario. For voice calling only (no chat), will I only be billed at the per user-minute rate, or also by MAU (and thus a subscription is required)? Thanks!

You can use only call by purchasing a call voucher without a chat subscription.
For your information, there is no call support in the developer plan, so chat should not have a subscription.