Voice over IP (VoIP) popularity and adoption is increasing with every passing day. Likewise, smartphone adoption is growing at such a rate that feature phones may soon be a thing of the past. Therefore, it was only a matter of time before VoIP started showing up on mobile devices and, just like with standard VoIP, it's a great way for the average user to save some money.

Obviously, Skype (News - Alert) offers this capability, allowing users to make calls over a data connection for a reasonable price, well below what mobile operators would charge. And, thanks to Microsoft's Skype Everywhere initiative, Skype is, well, everywhere — on the iPhone, iPad, any Android (News - Alert) device and, of course, Windows Phone.

There are other, more obscure alternatives available. Kakao Talk, for example, is a Korean-made app that began simply as an instant messaging platform, but has since added VoIP capability, allowing users to make completely free calls over a data connection. The only catch is that both users must have Kakao Talk installed on their device for this to work, so it takes some coordination to setup and relies on both call participants having a smartphone.

However, if you use a VoIP provider that doesn't have a mobile app, it's still possible, and pretty easy, to setup your device to make VoIP calls with pretty much any provider — at least with Android devices.

To begin with, just tap the menu button in the phone app and select "call settings" then "accounts" from the "Internet call settings" section. Next, tap the "add account" button and enter the appropriate information: user name, password and server information as provided by your VoIP provider. Some VoIP providers may require additional details in the "optional settings" section, but those providers should be able to guide you through that.

The menus may also differ slightly depending on what version of Android you're running.

As you can see, using a smartphone as a VoIP phone is really quite easy and the benefits are well worth the time it takes to set everything up — especially for those who make a lot of international calls.

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