According to the whitepaper (on page 18) it cost $70m to run Telegram just for 2017 and a total of $171m since 2014. Pavel Durov had a net worth of about $300m when he left VK in 2014 and as far as I know he's the only source of funding for Telegram. This seems like one way to change that and hopefully ensure financial stability, if it works out. I'm not sure it will though, which is unfortunate as I quite like Telegram.

There's always Wire, I suppose. As long as they stay afloat.