When The Verge broke the news yesterday that Facebook would be offering voice calling through its iPhone Messenger app, users happily accepted the gift. The app now lets users make unlimited free calls over Wi-Fi, avoid using up minutes by making calls over a 3G or 4G connection, and call numbers they neglected to save.

But why is Facebook doing this? The company did not respond to a request for an explanation, which is unsurprising since the feature was introduced without any fanfare at all. There was no formal announcement, no blog post. Is this part of a larger strategy, or Facebook adding a new feature simply because it can?

Both CNET and Forbes hypothesized that the new feature was added to boost engagement with teens, which sounds far-fetched given that teens prefer texting and SnapChat unless they're calling their parents. There's also no evidence that Facebook is working on speech recognition technology, the way Google did with its first voice offering, GOOG-411.

Facebook wants to be the way you communicate with your friends, period

Rather, Facebook wants to be the way you communicate with your friends, period — so it's offering a version of every medium that people use to do that, gradually blanketing all the venues where communication might happen. Think about it: on Facebook.com, you can instant message, email, and video call your friends. There's also the new Snapchat-esque Poke app for sending exploding photo-based messages. Facebook has been adding lots of updates to Messenger, which offers text messaging, voice memos, and now, voice calls. The social network even has wordless communication covered via its acquisition of Instagram.

Most robust messaging services, from Skype to Google Voice and on down, already offer options for voice calling. We can expect that the feature will be extended to the Facebook Messenger app for Android users, and will show up on Facebook.com as well. Facebook already has a billion users and the Messenger app is an easy install (Android users don't even need a Facebook account to use it), so this can only expand the company's reach while cultivating some goodwill among users.

It could also be considered the latest escalation in the ongoing cold war with Google, and has the potential to strain its relationship with Microsoft, which owns Skype. Facebook is looking to eliminate your need to look elsewhere for communication. That could be one reason for the quiet rollout. Microsoft and Facebook are pretty tight, so the former probably wouldn't be happy if the social network suddenly declared itself the only way to communicate (especially the same week of its big Graph Search announcement, which integrates Microsoft's Bing search).

This service could also be handy for Facebook in other ways. Most Facebook users have found themselves with a bloated friends list of acquaintances, coworkers, and near-strangers they met once. The company encouraged users to make lists to separate groups of friends, but the process is too much work and has never really caught on. Instead, Facebook has to triangulate in order to figure out who of your 935 "friends" is in your real-life social network — crucial information since an ad stamped with your best friend's face is likely to be more effective than an ad featuring the neighbor you spoke to just once.

By tracking who you call, Facebook learns who is in your real-life social network

Facebook says it isn't reading your messages or listening to your calls. But by tracking who you call most frequently, Facebook gains some insight into your social life in the physical world. "The best indicator of who I actually interact with socially the most in real life are the calls I make and the texts I send," TechCrunch's MG Siegler wrote in 2010. That's why Facebook came out with a dedicated app for messaging, and why that app is getting so much attention from the company. It also fits in with the company's neverending push into mobile, another way for Facebook to worm its way onto your phone without actually having to build a phone.

Some users wondered, on Twitter and in the comments of news articles, why Facebook had used its big international press conference to announce a search feature that isn't available yet instead of touting the new Messenger. But while voice calling is a nifty feature, for Facebook it was just the next logical step.