Vonage Holdings Corp plans to offer discounted international phone calls to iPhone and BlackBerry users, as the Internet telephony company aims to expand beyond the residential market.

Consumers could save more than 50 percent for calls to dozens of countries if they download a free Vonage application to Apple Inc iPhone and Research In Motion BlackBerry devices starting on Monday afternoon, Vonage Chief Executive Marc Lefar said.

It's an important first step for us. It moves us from the home platform, Lefar told Reuters. Over the long term mobile is absolutely a critical place for Vonage to be competing.

The service is available on any iPhone, which is available only to AT&T Inc subscribers in the United States, or any BlackBerry regardless of the carrier.

Computer-based Internet telephone services have been around for years, but mobile Web calling has come into the spotlight in recent months as Apple rejected Google Inc's Web calling service as an application for iPhone.

Lefar said Vonage was careful to follow all the application requirements set out by Apple and Rim.

Vonage users will even be able to make calls from iPhones using AT&T's cellular network as well as the device's short-range Wi-Fi links, found in places like coffee shops.

By comparison, usage of the iPhone app for Skype, the Internet telephone unit of eBay Inc, is limited to areas where Wi-Fi is available.

Vonage's iPhone customers, however, will use up minutes from their AT&T service plan whenever they make a call using the cellular network.

Lefar said consumers will still save a lot on international calls because they will pay Vonage's lower international rates rather than those of AT&T.

He said there are differences in how the application works on both iPhone and BlackBerry.

IPhone users will have to open the Vonage application every time they want to take advantage of its cheaper rates, while a BlackBerry will automatically revert to the Vonage rates over the wireless provider's every time an international number is dialed.

Initially, users will have to prepay for Vonage mobile calls and will be charged on a per-minute basis, according to Lefar. He said that Vonage will also offer a flat monthly rate soon.

(Reporting by Sinead Carew; Editing by Richard Chang and Leslie Adler)

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