Facebook rolled out a new feature for the Messenger app on iPhone that lets you make free phone calls to your friends using a WiFi or cellular data connection.

There are, of course, a few caveats:

• It only works on iPhone.
• It only works in the U.S. and Canada.
• Both parties need the separate Facebook Messenger app to make calls. It won't work with the regular Facebook app that you use to update your status and check your News Feed. 

But the calling feature in Messenger hints at the grander plans Facebook has for you phone. Just like Facebook is increasingly doing everything in its power to keep you stuck on Facebook.com on your desktop (the addition of search last week is a big step), it's becoming clear that it's also doing its best to keep you within its app ecosystem on your smartphone, even when making calls. 

The calling feature works really well too. I've been using it all week to make calls, and the quality is a lot better than it is using the regular calling feature over Verizon's network. In some cases, audio sounded a bit tinny if the person on the other line was using a 3G connection instead of WiFi or LTE. But overall, it was a great experience. 

So what does the future "Facebook phone" actually look like? Matt Lynley of the WSJ says the phone might already here, but I think there's a lot more work to be done before we can make that call.

I have a few ideas.

First and most importantly, I'd like to see Facebook redesign its regular app as an all-in-one app. Right now, Facebook has separate apps for sending messages (Messenger), uploading photos (Facebook Camera), managing Like pages (Facebook Pages Manager), and sharing self-destructing photos and videos with your friends (Poke). TechCrunch's Josh Constine says Facebook is working on a redesign for the app (he's seen it with his own eyes), so hopefully that app will spin in features that have been relegated to separate apps. 

The calling feature needs to be more phone-like. As it works now in Messenger, you have to select your friend's name, then press a the "i" (information) button to get the phone call option. Phone calls appear on the recipient's screen as a regular pop-up notification if Messenger is closed, so it can be pretty easy to miss a call. Even though Messenger can be used as a phone replacement, it doesn't have the look and feel of one yet.

And finally, Facebook just gave us a glimpse at a future where all smartphone features are performed over data connections. Your regular cell phone plan for calling and texting is slowly dying. Trust me, carriers realize this. The two biggest carriers, Verizon and AT&T, are happy to give you unlimited regular texting and calling in favor of charging you up the nose for data usage.

Despite Mark Zuckerberg's denials, there's always a chance that Facebook will release its own smartphone one day. We already know based on several reports that the company is at least working on one. However, last week's update to Messenger makes me think it'd would be just as happy turning every phone into a Facebook phone through its apps. It feels like a very Facebook-y move.