Line has reached 20 million just 8 months after it first launched, charting some notable figures along the way. NHN built and first marketed the application in Japan — which was the first overseas market it ever expanded into — and it has revealed that Line is seeing one million new downloads worldwide each week, and February alone saw it add an impressive 5 million. 

As recently as 2010, growth in US Facebook usage was well into the double digits, at 38.6%, eMarketer estimates. But with 116.8 million US internet users already logging on to the site at least once monthly that year, growth rates were bound to plateau.

By 2011 Facebook user growth rose a comparatively small 13.4%, and this year will be the first when growth rates drop to the single digits. Rates of change in the US will continue to decline throughout eMarketer’s forecast period.

On Twitter, by contrast, growth is stronger. Last year’s 31.9% increase in users outpaced that of 2010, when growth was at 23.5%. Similar to Facebook’s trajectory, Twitter’s growth rate will also fall in the coming years, but still remain nearly four times higher than Facebook’s growth rate in 2014.

Twitter’s size, which is fairly small, is one factor that makes such growth rates possible. Facebook already reached an enormous audience of nearly 133 million US internet users at the end of 2011, a figure that will surpass 150 million by 2014. Twitter, in comparison, had a US user base of less than 24 million at the end of last year. Still, between 2010 and 2014, eMarketer predicts, Twitter will about double its US user base, reaching 37.6 million microbloggers by the period’s end.

More Smartphones than Humans by end of year

A prediction for the future of smartphone growth makes some bold projections: By the end of this year, there could be more smartphones on the planet than humans, and by 2016 there could be 10 billion smartphones. That’s 1.4 mobile devices per capita.

In its global mobile data traffic forecast, Cisco predicts that a solid chunk of growth will come from the Middle East and Africa, with a compound annual growth rate of 104%, followed by Asia Pacific with 84% growth.

What will people be doing with their smartphones in the coming years? Cisco predicts that by 2016 two-thirds of the world’s mobile data traffic will be from videos, increasing 25-fold between now and then. Mobile network connection speeds will increase as well, according to the company.