WhatsApp, the world’s most popular messaging service, is dropping its token $1 a year subscription fee for consumers as it experiments with making businesses pay to send notifications to consumers, Chief Executive Jan Koum said on Monday. The seven-year-old company, which was acquired by social media giant Facebook (FB.O) for $19.2 billion in 2014 and now counts nearly 1 billion users, is testing making restaurants, airlines and credit card companies pay to contact consumers, Koum said.