WhatsApp is changing its policy as it begins building a moneymaking business after long placing little emphasis on revenue. The company plans to allow businesses to contact customers directly through its platform. A similar strategy is already being tested on Facebook Messenger, a separate messaging service Facebook owns.

“We want to explore ways for you to communicate with businesses that matter to you, too, while still giving you an experience without third-party banner ads and spam,” WhatsApp said in a blog post announcing the changes to its privacy policy.

Among the changes, Facebook will be able to use a person’s phone number to improve other Facebook-operated services, such as making new Facebook friend suggestions, or better-tailored advertising, WhatsApp added. It said the data-sharing would also be used to fight spam text messages across its service.

WhatsApp emphasized that neither it nor Facebook would be able to read users’ encrypted messages and that individual phone numbers would not be given to advertisers. WhatsApp users are still required to provide a phone number only to sign up for the service, and can opt out of giving it to Facebook.

While WhatsApp operates autonomously from Facebook, Mr. Koum sits on Facebook’s board.

The changes were immediately viewed with a critical eye by some who were concerned when Facebook bought WhatsApp that their data could one day be misused. WhatsApp made early inroads with people worldwide partly for its hard-line stance on privacy and individual liberties, which was rooted in Mr. Koum’s youth in the 1980s in the Soviet Union, where, he has said, he lived in fear of his communications being monitored. Mr. Koum has also been outspoken against advertising in the app in general.