One of the the WhatsApp founders, Brian Acton, donated $100 million to them as an unsecured loan due to be repaid in 2068:

https://en.wikipedia.org/wiki/Brian_Acton#Signal

https://en.wikipedia.org/wiki/Signal_(software)#Developers_a...

How long does that last? Telegram uses a few hundred million dollars each year, although they are significantly larger.

> As Telegram approaches 500 million active users, many of you are asking the question – who is going to pay to support this growth? After all, more users mean more expenses for traffic and servers. A project of our size needs at least a few hundred million dollars per year to keep going.

https://t.me/durov/142

> needs at least a few hundred million dollars per year to keep going

I'm pretty sure that is not server cost. This is probably the standard approach of companies hiring tons of personal and spending tens of thousands or hundreds of thousands on ads every single day.

They recently added support for in-app donations: https://www.theverge.com/2021/12/2/22814934/signal-launches-...

I hope they'll take it a step further and require payment for certain functionality (maybe video calls?, or desktop client support?).