Hail Protocol v1.0: A Federated Async Telephony Protocol with User-Owned Metadata Audit

The Hail Protocol describes a federated, transport-agnostic protocol for asynchronous telephony — voice and SMS — in which recipients are network-invisible (never SIP-REGISTER), inbound contact is mediated through user-chosen rendezvous channels, and every signaling event is witnessed in a tamper-evident HNBP-CORE hash chain on the user's own device. Version 1.0 specifies five transport modes (PSTN-bridged, self-hosted gateway, federated peer-to-peer, onion-hidden, and chat-carried) and provides reference implementations for SMS Mode A and Mode B, both integrated with the Number Stations 2.0 cipher (DOI 10.5281/zenodo.20042412) for end-to-end encryption. The protocol is novel in three respects: (1) the inversion of the SIP registration model, replacing always-on presence with async ticket delivery; (2) the bring-your-own-infrastructure deployment pattern, eliminating central servers and removing AriaLabs from the metadata path entirely; (3) the per-event tamper-evident audit chain, providing the user (not a vendor) with cryptographic proof of communication history. Published as defensive prior art.