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It's not really "pop" technology. Surprisingly, it's not used much in the United States, but in India it's basically a replacement for text messaging. Everyone from a 13 year old child to my grand mom uses it to keep in touch with friends and family members across the globe. IMHO, they were able to get to such widespread everyday usage because they such awesome and reliable technology. Much better than what Google ha…
I thought it was the de facto messaging app across the world? Is there any particular reason why it is not used much in US?
This is why, IMO, Apple, Google and Facebook are the only companies really in a position to change the messaging game in the US. There is space for newcomers (see: Snapchat), but they're going to have to work hard to spread beyond their initial niche.
Apple is driving iMessage adoption via iOS, albeit mostly only for messaging between iOS devices. Facebook has a solid mobile install base already, but they can't seem to figure out how to convince users to use Facebook messaging. It actually works really well for me, but no one I know actually uses it.
Google seems to be in the process of merging Hangouts and SMS. They're already the same app on Android, but you get to pick the protocol. Their logical endgame is to move all messaging to the Hangouts protocol, and fall back to Google Voice to deliver messages to users who don't have a Hangouts client.
If Google can pull this off I think they're going to absolutely kill it, but they seem to be having a lot of execution problems.