By Allan Kamau, Head of Portland Nairobi, Special to CNN Editor's Note: Allan Kamau is Head of the Nairobi office of Portland, a strategic communications consultancy which has released a study analyzing geo-located tweets from Africa's 20 most populated cities during the last three months of 2013. The study looks at which cities are the most active, what languages are being used the most and what subjects are driving the conversation online. Portland's latest research on How Africa Tweets can be found at: www.portland-communications.com. For the purposes of this story, Portland's infographic has been re-cropped to fit CNN's template. The opinions expressed in this article are solely of Allan Kamau. Africa is experiencing an extraordinary transformation but few areas have seen such fundamental change as communications. Thanks largely to the incredible rate of adoption of mobile phones, the way people speak to each other, share opinions and access information and services has been revolutionized in a handful of years. Business consultancy McKinsey estimates that more than 720 million Africans out of a population of one billion now have mobile phones. The rise of smartphones means that 167 million already use the internet and 52 million are on Facebook. The figure is increasing fast by the day.