Not an easy question to answer without knowing where in the world you are using your device from as this can differ.
Below is a Google Nest help center link that describes the calling options available.
If you need any further assistance please let us have us much relevant information as possible so we can try to help you further.
Thanks for visiting the Community.
We appreciate your help on answering this thread, Cathal_S.
@JedBarker, calling feature is only available to the supported countries where Google Nest Hub Max is launched. Hope the link provided by @Cathal_S answered your questions. Feel free to update this post, otherwise we'll be locking the thread.
Due to inactivity, I'll go ahead and lock this thread in 24 hours. Feel free to start a new thread if you need assistance with your Google speakers and we'd be glad to assist you further.