Vonage has become a veritable player in the home phone industry in the US, thanks to ultra-cheap rates for its Voice Over Internet Protocol calling system. Now it’s making that service mobile via Android, and making a real case for VOIP-based service, if not VOIP-only phones. Customers who subscribe to Vonage at home can make domestic calls to anyone else with the app for free, and even those without an existing account can use the app to make calls to regular cell and landlines on a per-minute basis, Skype-style. The best part? It works on WiFi or mobile broadband, making Vonage a true mobile VOIP provider with no restrictions.

Other little touches surround the well thought-out app: a background service keeps an eye out for incoming calls to your Vonage number, and it integrates with your existing address book to check if you can call other Vonage customers or app users for free. Basic texting is included at no extra charge, much like the recently updated Google Voice. According to the app’s Android Market description, calls to to any number in the US, Canada or Puerto Rico will be free for a limited time… no matter where in the world your call originates.

There are a few restrictions. Calling when connected to a mobile network uses data instead of minutes, so using Vonage to completely replace your cell phone plan could get expensive fast. And the free US and Canada offer is limited to 3000 total minutes a month – though if you’re talking on the phone for 50 hours over 30 days, you’ll probably appreciate the gesture anyway. On that note, one impressive convenience feature is that you can add pre-paid calling credit directly from your Android Market account. Download the Vonage app for free here.