TransUnion This document specifies a means for a third-party service to prove and attest the association of a communications platform with a particular user's telephone number. This capability supports secure enrollment for users of messaging platforms or similar real-time communication applications, for cases where users assert telephone numbers as communication identifiers, and interoperating platforms need to verify that identifiers are being properly attested. This general approach can potentially work with other forms of Service Independent Identifiers (SIIs) in the More Instant Messaging Interoperability (MIMI) framework.