Always interesting to track the mobile mobile messaging apps. They have the potential to play a major role in the discovery of content and apps, they're taking a significant share of mind away from Facebook and they're still somewhat under the radar. But some of them are very big. (I'd include Line and Wechat, but the former isn't a useful search term and Google doesn't accurately reflect Chinese search volume for Wechat).
And, of course, the survivors from the previous generation of mobile comms, most of which focused on interconnection with the PSTN, combined with roaming arbitrage, and none of which really went anywhere in the end, especially compared with the new generation.
And then there's a puzzle. Google Trends is obviously a little unscientific, but I do wonder why Viber shows up so far behind Whatsapp when it claims almost as many users.
Finally, remember Vonage? Google Voice? And, for comedy value, Hangouts?