Hi Stephan,
You can list down the Meeting Templates under your Account from here.
But I'm not sure what is the exact initiative/task to check for Calling and Messaging Template, because currently we don't have any such API endpoint to support this requirement. However, for Calling and Messaging, it's pretty much constant and doesn't require any specific setup to continue with these 2 services.
And, for your second query -
how can I apply them to a person using the APIs
At least for the Meeting Template, you can't assign it to any specific person that way. You can use a specific templateId though when you're creating-a-meeting through this API.
During the meeting-create, you can apply the templateId you want and that'd be applied for all the invitees for that meeting.
Please let us know for any further assistance on this by replying on this thread!
Kind regards,
Sandip