If you need to stay in touch with relatives in far away lands, Vonage just released an Android app for you. You can now use the Vonage VoIP system on your Android phone to make free international calls. Of course, it's not completely free... you need to have one of Vonage' VoIP international calling plans to use the app. Their Vonage World Plan is only $15 bucks a month, which is a lot cheaper than racking up per minute charges, if you call family often.
One nitpick with the app is that it doesn't support messaging like some other similar apps, including Fring and Viber; however, if you are already an existing Vonage customer, this should prove very useful to you.
Source: Engadget and Android Market - Vonage Android App