phone_number payload on Create identity) or later on an existing identity via Provision phone number with agent_handle. Once attached, the number stays bound to that identity for its lifetime. Each identity supports at most one phone number, and that number is dedicated to that identity — there is no reassignment between identities.
To release a phone number, either delete the identity (the linked number is released as part of the cascade), or use the endpoint below to release the number while keeping the identity active.
Release phone number
204 No Content on success.

