Recently, Whatsapp need to charge some of their android clients. As an Android developer, that is not a bad things. Most of android client ever bought anythings from Google Play. I believe there will be a number of users need to enter their payment details. After that, if they want to buy other paid app, they just need to click and their password again. That is easier. Moreover, after their first times to buy a paid app, they may think that is not too bad to spend one or two dollars for buying an app. That is good for us.