Making cheap international calls from an iPhone just got a whole lot easier.

Vonage Holdings Corp. announced Monday an Internet phone-calling application that can be downloaded for free to iPhone and BlackBerry smartphones allowing international calls through Wi-Fi or cellular networks.

In addition to iPhone and BlackBerry devices, it will work with iPod Touch devices, which connect via a Wi-Fi network, Vonage said.

The application, which works on both cellular and Wi-Fi network connections, not only allows users to take advantage of low rates for international calling, but also uses VoIP capability when on a Wi-Fi network to avoid using your phone plan’s minutes.

The application, Vonage Mobile, was available for free today at on the company's Web site and the iTunes App Store.

The iPhone will allow a Vonage call on both cellular and Wi-Fi networks, while BlackBerry devices will make Vonage calls via cellular networks.

For the Vonage portion of the call, international rates will be extremely competitive with rival Skype, according to Vonage. Skype offers Internet calls from iPhones, but only via Wi-Fi, a service it started earlier this year.

There is no monthly service fee for Vonage Mobile, although the company plans to launch a Vonage World plan for mobile later this year at a set monthly fee to make unlimited calls to more than 60 countries. The company did not announce the amount of that fee.

Software Iphone App