These days, a conventional phone number is becoming less and less vital. As e-mail, IM, texting, and other methods of Internet-based communications take hold, getting in touch with someone (even via voice) doesn't actually require a phone number and voice services.
Facebook's latest
iOS app update is proof of that, with the new edition rolling out live voice calls to other Facebook members. You'll need to have friends in the U.S. and Canada, have a solid data connection, and a few good things to talk about. It's a feature pulled over from Messenger, and while it has yet to be implanted into the Android / Windows Phone versions of Facebook, we're guessing those will hit soon after assuming the iOS rollout goes well.