Making international calls can be expensive, and calling rates for certain countries just don’t seem to be getting any cheaper through traditional calling plans. Fortunately, VoIP (Voice over Internet Protocol) apps can modify the way calls are made from your phone and reduce the cost of each call.

Two of the most popular VoIP apps are Rebtel and Viber. International calls can be made using either app, although there are some key differences between the two.

- Rebtel was founded in Sweden in 2006 and rapidly grew to become the biggest international call provider next to Skype. Rebtel has a great app that works on Android phones and tablets, iPhones, iPads, Windows phones, most other Smartphones and even older mobile/cell phones and landlines! Rebtel offers incredibly inexpensive international calling even to non-Rebtel users by creating “local” landline numbers in each country so the international portion of the call costs less than calling with a calling card or using a traditional mobile carrier’s international calling plan. Rebtel also, constantly monitors whether the 3G network or local Wi-Fi is the better signal, and switches seamlessly between the two to keep the call active without defaulting back to a regular billed call using your phone company’s rates.

- Viber was launched in 2010, and was originally intended to be a competitor for Skype specifically targeting the iPhone market. It has slowly increased its reach, and can now be downloaded to newer Android phones, iPhones, Windows phones, Blackberry devices and personal computers. Viber offers free calls between Viber users, including Viber international calls, but the biggest consumer complaint is that calls can be switched to a regular cell call mid-conversation if the internet connection is interrupted. This can result in huge phone bill charges due to the high cost of international calls through mobile carriers.

Real Life Example: Viber International Calls vs. Rebtel International Calls

For example, during a Viber international call, the 3G internet connection being used to handle the call could be lost. The call switches to the standard mobile network, and suddenly a call that was free is costing 33 cents per minute. The user doesn’t even know about it until they receive their phone bill.

In contrast, a Rebtel user in the same situation might lose their 3G connection, but the app will automatically switch to the local available Wi-Fi and the call will continue. Even if the call is placed to a non-Rebtel user, the low international rate still applies instead of switching to the high rate from the mobile carrier.