Facebook just rolled out its free VoIP voice calling feature to U.S. users of its Facebook Home and Facebook Messenger app.

This means that Facebook expands even more into users' personal space and now all iOS and Android users in the U.S. can forget about the standard "phone" and just use Facedial instead to call their friends.

VoIP for Android was previously available in 23 other countries, which are now 24 with the new rollout to the U.S. According to TechCrunch, the rollout was scheduled for Thursday, April 18, and does not require any formal app updates.

Starting a VoIP call in Facebook Messenger is fairly easy: just click the "I" icon on a friend's profile and tap "free call." In the new Facebook Home, meanwhile, users can start a call from a Chat Head by clicking the three dots near a friend's name, opening the conversation in Messenger, and follow the same steps as for Messenger.

Facebook first started its open source version of VoIP for iOS in Canada and the U.S. back in January, and since then it continued to roll it out gradually to more countries and the Android platform. The availability for Android users in the U.S. marks the peak of this rollout.

With VoIP now available to all iOS and Android users in the U.S., users no longer have to worry about the devices their friends are using. This marks an important step for Facebook and a major milestone in its bid to fight Google and Apple to control messaging. Google is widely expected to launch a unified messaging system soon, combining GChat, Google+ Messenger, Google Voice and potentially Gmail to allow users to carry synchronous and asynchronous text and voice conversations across various devices. Apple already has its own iPhone app on its smartphone and its iMessage apps on several other platforms.

The bottom line is that despite the fact that smartphones nowadays are basically miniature computers, their fundamental function is still communication. A smartphone may have loads of apps and features, but if it can't serve its main communication function, it's pretty much worthless. Communication takes a lot of users' time, and whoever controls messaging owns that time. Meanwhile, this area presents a great opportunity for advertising and monetization through sales of sticker packs and more. In other words, companies win over fans and advertise more, while consumers are able to place free calls and communicate easier. Win-win?