For mobile users who text with friends via Facebook, it's almost time to download the social-media giant's dedicated app for doing so, or lose the ability.

Facebook says that, for the next few days, it will be notifying people that if they want to continue sending mobile message, they'll need to download the Messenger app.

"As we've said, our goal is to focus development efforts on making Messenger the best mobile messaging experience possible and avoid the confusion of having separate Facebook mobile messaging experiences," a Facebook spokeswoman said Tuesday in a written statement.

"Messenger is used by more than 200 million people every month, and we'll keep working to make it an even more engaging way to connect with people."

In April, Facebook announced the change was coming. It has been rolled out to Android and iOS users in parts of Europe and elsewhere since then, and is now coming to the United States.

In November, after Facebook launched Messenger 3.0, the company discontinued messaging in the core Facebook app for people who already had Messenger.

The good news for people still using just the Facebook app is that they'll be able to message friends in much the same way they do now. Once both apps are installed, tapping the "message" icon on the Facebook app will simply send the user to Messenger. They'll be able to return via a "return to Facebook" icon.

The popularity of apps like Messenger and WhatsApp, whichFacebook purchased in February, are helping change the rules for texting. Wireless plans that charge for texting are becoming a thing of the past in the United States, though they remain the norm in places like India, South America and Africa, where WhatsApp has become a popular, nearly free alternative.