$500M/yr in raw revenue? How do you grow from there? Lower costs? Grow your revenue? Half a billion is getting close to max adoption. Do you up your prices?
Once I get there I can solve other problems as they come up. Would that be a reasonable approach?
Simple phone messaging, not likely.
But where does phone messaging lead to?
• Other comms services (voice, voicemail, teleconference, video). There's room for improvement in all of these. Look at the one stand-out from G+: Hangouts.
• Sales or transactions. From text messaging to commerce-via-text is a step. Or banking. Both are directly monetized.
• Some level of community-based information service with a commercial component. I've long wondered why more of the social networks haven't gone here.
Or, of course, "get bought by Facebook".
The key though is that Telegram actually isn't free to consumers when compared to Whatsapp. At $1/year + access to everyone who is already on network vs. $0/year + access to smaller network+need to invite your friends to build that network Whatsapp is actually (significantly) cheaper. If it was more expensive per year I think they'd be giving some room, but no one is even going to notice getting billed.
And although there is likely a slow take up by the elderly, the next generation are all new customers. The 1/5th smartphone ratio can only go up. (This POV is of course assuming WhatsApp wins the messaging war, which is what FB is betting on)