Facebook is phasing out the mobile messaging feature on its Android and iPhone apps, essentially forcing users to download a standalone Messenger app.

This means that people must now download and register a separate app to do something that was already in the social network's mobile service. 

Users were notified of the changes a few weeks ago, with an alert that said that sending messages inside the Facebook app would soon be disabled.

The company first took out the messaging function in its main apps in a few European countries, including England and France, last April. At the conclusion of what the company claims to be a successful test period (Facebook claims that users replied 20 percent faster with Messenger), the service is being rolled out to users around the world, who now have to pull up a different app to read and respond to messages from friends.

Forcing 1.2 billion users to suffer through such an inconvenience may incite a rebellion against Facebook's sudden service overhaul, and the company seems to be aware of the possible backlash. Unlike every other service change from the company, the phasing out of the messaging feature was not announced with a press release, perhaps in an effort to keep publicity at a minimum.

Nonetheless, several news outlets have spotted the changes, and Facebook has responded with an official statement. 

"We're continuing to notify more people that if they want to send and receive Facebook messages, 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 separate Facebook mobile messaging experiences," the company said. 

The changes are expected to kick in over the next few days. If users attempt to use messaging inside Facebook, a prompt would pop up that tells users to download the Messenger app. Pending messages would still be viewable inside Facebook. However, to reply, users must log on to Messenger. The service change only affects Facebook's Android and iPhone users. Windows Phone, iPad, mobile web and desktop users can still send messages inside Facebook.