Signal has long had a privacy contradiction at its core: the most secure mainstream messenger still required a phone number to sign up. That number became a de facto identity anchor, linkable to you even if you never shared it with contacts. Signal has now added an optional way around that, and zero-knowledge proofs (ZKPs) are part of it, though not in the way most coverage suggests. Phone-numberless registration landed in the Signal Android 8.28.0 beta on 16 September 2026. It is optional, Android only, and it costs a one-time in-app purchase: 3 USD in the United States, with per-country differences, checked 29 September 2026. The zero-knowledge proof is not what replaces the phone number. It is what stops Signal from linking that purchase to the account it creates. This post breaks down what Signal actually built, and what self-hosters can and cannot take from it.

💡 Why This Matters

Phone numbers are lousy identifiers for a private messaging app.…