I don't really see how your first sentence is related to the second!
I'd suggest the reason for the valuation is exactly because we had this in the 90s (and earlier really) and it never made the transition to digital until now. So the market has somewhat been proven.
They might not be related but the second one is a relevant question I think.
This looks like a good example of investing in the founders, not in the business. The business is very WTF, but the article makes the founder sound like a known quantity.
This was basically my reaction, but the enabling tech is definitely not the same thing as the product. It seems like they're betting on the founders to find the right approach to make it an Instagram for voice (Instaphon?)
Maybe they have super high engagements per day - like twitter's early days?