Most apps that allow for free international phone calls require that both parties download the same app.
That's why Facebook Messenger is a good place to start since so many people already use the service.
Messenger is a separate free app from the regular Facebook app, but it has the same interface and ease of use.
Through this app you can text, record voice messages, and make phone calls to other friends through the app.
if you're always logged in, you'll never miss a message.
Facebook is also the owner of WhatsApp, another free phone call and texting service.
People love WhatsApp because it works on almost every type of phone and allows you to send photos, messages, and make phone calls for.
Free over a wireless network.
Lee Von and Vibra are two other similar services worth checking out.
Both use their data plans to send and receive messages but don't charge you for actual minutes spent talking.
And finally, if you're looking to make video calls it's hard to beat Apple Space time for iPhone users or good old fashioned Skype.
In San Francisco, I'm Kara Suboy CNET.com for CBS news