There's a temptation to make trust proprietary — to have each voice platform vouch for its own agents. But verification issued by the party being verified isn't verification. It's marketing with a checkmark.
The web solved this with certificate authorities that sit outside the sites they vouch for, operating against an open standard anyone can inspect. Trust worked precisely because it wasn't owned by the thing being trusted.
That's why the Voice Trust Protocol is public. Anyone can implement it, anyone can verify against it, and no single vendor — including us — is the arbiter of what's real.