Hi Phil:
I am the Product Owner for Authentication 365. Thank you for reaching out. You are correct in that to use Authentication 365 as an option to SAP IAS, you'll need to have an Authentication 365 account first. You'll also need to have an SMS Account as well to deliver the SMS messages with the validation code and message (all customizable in SAP IAS).
I will reach out to you directly via email and we can continue our conversation.
Best regards,
Bill
William Dudley Head of Mobile Innovations & Evagelism,
Sinch