[kelnage]

Telephony is federated, in some senses. But not as is generally accepted when speaking about internet communication protocols. Compared to SMTP or IRC, the average person can't start their own telephony service provider - to do so is highly regulated and involves organisations such as the ITU. I'm sure, given such an infrastructure, Signal could be relatively easily moved to a "federated" set-up. But that wouldn't solve the issues that people who complain "Signal isn't federated" want fixed.