This topic has been around for years. WhatsApp is going to charge users yearly for using the service. There was no actual action from WhatsApp until recently when news of the subscription model began to circulate.
Currently, iOS users need to pay just a single US$0.99 to download the app. Based on the source information, in the near future, new iOS users will need to pay annual fee to use the service (same as Android).
With more and more similar services in the market (Kaokatalk, Line, WeChat and etc) providing free services, it may just shift some users to other services.
For me, if I have to pay annually for the service, I may just switch to another one in the market. Let me know what you think? If you cannot live without WhatsApp, I would love to understand what is the attraction or what is the unique feature(s) that attracts you.