If you've been putting off calling your aunt in the Dominican Republic or your Slovenian cousins because of the cost of calling from your mobile phone, a promotion from Vonage should pique your interest. The VoIP provider is giving away one free international phone call, up to 15 minutes, to anyone who downloads its new iPhone app, Time to Call. The app is also free.

What's especially appealing about the offer is you don't have to be a paying customer of Vonage (from $11.99 per month) to use the app or get the one free trial call. The free call expires one year after you download the app. Be sure to check that the country you're calling is on the list of 100 that are included in the deal (check below).

After your one free call, all calls are billed in 15-minute increments. Prices for the 15-minute blocks of international talk time range from 99 cents to $9.99, depending on which country you call, although calling most countries is less than $1.99. And typical of Vonage's slightly experimental nature, the Time to Call app doesn't charge you through pre-paid credits or an in-system account, the way other services such as Skype do. Instead, Vonage's app bills you directly through iTunes.

The app is available as of today in 87 international iTunes stores. It works best over WiFi, but in the U.S. and Canada, it also works over a 3G network.

"With the launch of Time to Call, Vonage has simplified the process of making affordable international calls for iPhone users around the globe," said Marc Lefar, CEO of Vonage. "Not only does this service offer tremendous value for international callers dialing from their home countries, it also provides a great solution for international travelers who want to avoid the bill shock associated with international calls and roaming charges when they call back home. Time to Call requires far less effort than calling card services and other international calling plan options, and is substantially less expensive than dialing direct through a mobile carrier. It's simple, fast, and fair."

As with any phone service, keep an eye out for additional fees, such as taxes and tacked on data fees from your mobile provider.

Eligible countries on the list of 100 include: American Samoa, Angola, Argentina, Australia, Austria, Bahrain, Bangladesh, Belgium, Bermuda, Bhutan, Brazil, Brunei, Burundi, Cambodia, Canada, Cayman Islands, Chile, China, Colombia, Costa Rica, Cyprus, Czech Republic, Denmark, Dominican Republic, Egypt, Finland, France, French Guiana, Georgia, Germany, Greece, Guadeloupe, Guam, Hong Kong, Hungary, Iceland, India, Indonesia, Iraq, Israel, Italy, Japan, Kazakhstan, Kenya, Kuwait, Kyrgyzstan, Laos, Latvia, Lithuania, Luxembourg, Macau, Malawi, Malaysia, Malta, Martinique, Mexico, Mongolia, Montserrat, Mozambique, Nepal, Netherlands, Netherlands Antilles, Nigeria, Northern Mariana Islands, Pakistan, Panama, Paraguay, Poland, Portugal, Puerto Rico, Reunion, Romania, Russia, Rwanda, Saint Barthelemy, Saint Martin, San Marino, Saudi Arabia, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, Taiwan, Tajikistan, Thailand, Trinidad And Tobago, Turkey, Turkmenistan, Uganda, U.K., U.S., U.S. Virgin Islands, Uzbekistan, Vatican City (Holy See), Venezuela, Vietnam, and Zambia.

This article, written by Jill Duffy, originally appeared on PCMag.com and is republished on Gear Live with the permission of Ziff Davis, Inc.