Vonage estimates smartphone users can save more than 50 percent on calls to many countries, compared to current wireless carrier rates. Vonage is also pointing to convenience. Cost-conscious consumers can dial direct from the phone rather than using calling cards for lower international long-distance rates.

"Our new mobile app is an important step in establishing Vonage as a software technology company that enables high-quality voice and messaging across any device in any location, providing great value over any broadband network," said Marc Lefar, CEO of Vonage.

Vonage Mobile for Globe-Trotters

Vonage Mobile lets globe-trotters call home from wherever they are or make calls from home base to friends, family and clients in dozens of countries. Vonage aims to make it easy, with no access numbers or distinct phone numbers to give to friends and family.

Here's how it works: Smartphone users enter an international number or select a contact from the contact list on the iPhone or BlackBerry and hit send. Vonage works behind the scenes to make the international connections. The rates are lower than both traditional wireless and landline carrier rates and allow calls on the go. For example, smartphone users pay two cents per minute to call China and between two and three cents a minute to call Germany.

In the fourth quarter, Vonage plans to enhance the app to include its Vonage World plan that was introduced for home service in August. Vonage World will let users make unlimited calls to more than 60 countries for one flat monthly fee.

"When developing Vonage Mobile, we focused on creating a more convenient alternative for customers who use calling cards or Wi-Fi-only applications," said Mike Tempora, senior vice president of product management for Vonage. "Vonage Mobile is easy to get and use, and gives customers the best possible calling experience from a trusted provider."

What About Google Voice?

William Ho, a wireless services analyst at Current Analysis, said the mobile app could help Vonage retain customers who may be leaving and build new customers. At least for now, the mobile app is a marketplace differentiator.

"This is good for the Vonage user, especially if they are international callers," Ho said. "Vonage is offloading the calls using the data channel over Wi-Fi or cellular. For the customer , that means they don't have to be in their house to make international calls over Vonage. That's a benefit."

But what about Google Voice? Google tried to get its Google Voice product on the iPhone and was rejected. Based on the known details of the Vonage mobile app, Ho said it doesn't appear that Vonage is making a full data call -- it's just voice minutes. If that's the case, he said, the calls are not circumventing the carrier's minute bucket.

"You have to look at this from the AT&T context. So from a PR to the FCC standpoint, Apple can say it let Vonage through," Ho said. "Vonage is palatable because Vonage is a known carrier, whereas Google is not a known carrier."