The Time to Call app, which is free to download from the iTunes app store, and easy to use. Simply select the country you want to call, touch the Buy button then enter you iTunes login details. Users can now make the call either from their address book or by directly dialing the number in the usual manner.
Calls to 100 countries including Greece, Spain and the US are charged at a flat rate covering the whole 15 minutes with prices ranging from $0.99 to $1.99 (£0.60 to £1.20). Meanwhile a further 90 countries are also available and flat rate calls to these numbers cost up to $9.99 (£6)
"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 dialling from their home countries, it also provides a great solution for international travellers who want to avoid the bill shock associated with international calls and roaming charges when they call back home."
Vonage revealed users can make one international call for free as part of a trial of the app, which will be available for a limited period.
Vonage also revealed an Android version of Time to Call will be made available later in the year.
Last year, Vonage launched a voice over IP (VoIP) application that allows users to call each other from their Facebook page without the need for either caller to disclose their phone number. The Vonage Mobile Facebook application can be used on either an Apple iPhone or a Google Android smartphone and costs nothing to download and install.