Internet phone company Vonage brought a smartphone version of its Voice over IP (VoIP) calling service to the BlackBerry and iPhone today. The free, downloadable app promises to provide seamless, low-cost international calling while on Wi-Fi or cellular networks.

While the iPhone allows VoIP calls on both cellular and Wi-Fi networks. IT redirects the former to a local access number so as to charge users for AT&T minutes used when Wi-Fi isn't available, however. If it allowed you to use the carrier's 3G or EDGE network, you wouldn't be charged anything beyond your standard Vonage rate. But, apparently, this is the compromise Vonage had to reach to make it into the iTunes App Store.

iPod touch allows VoIP calls over Wi-Fi networks only, of course. The BlackBerry version of Vonage Mobile works only over the voice network like the iPhone, and it does not support Wi-Fi for some reason.

Below is a list of features of the new mobile app highlighted by Vonage:

-- Rates are better than traditional wireless and landline carrier rates
-- Lets you make calls while on Wi-Fi or cellular networks, providing full mobility
-- Uses your existing contact list - just click and dial - no extra steps
-- Utilizes your existing cell phone number so the people you call will recognize who is calling
-- Real-time balance updates and the ability to automatically replenish funds in your account
-- No more trips to the store to buy calling cards, no 800 numbers or access codes, and no connection charges

In the fourth quarter 2009, Vonage plans to enhance the app to include support for the Vonage World plan introduced in August. Until then, it is play-as-you-go only.

See here to learn more about Vonage Mobile and here for directions on how to download the app.