The market for VOIP apps is certainly crowded. While Skype and Google Voice have already established themselves as great apps, it’s always good to see what else is out there. That’s why on this edition of App of the Week, I’m covering the new Vonage Mobile app available for both iOS and Android. It takes a little bit of what Google Voice does and a little bit of what Skype does to create a unique package with some interesting features that definitely make it worthy of a spot on your smartphone.

Platform Availability: iOS 4.0 and up. Android 2.1 and up.

Cost: Absolutely free! Download it here for iOS and here for Android.

What it is: An app that tightly integrates with your phone’s address book to make free calls and send free texts to other Vonage Mobile app users, along with super cheap international calls/texts. And for a limited time, all calls to the U.S., Canada, and Puerto Rico are free!

How does it work: Install the Vonage Mobile app onto your phone. After firing it up, it will ask for your phone number and email address. You will receive a text giving you a number to verify your account. If you can’t receive SMS, you can opt for Vonage to call you as well. After setup, make calls/texts to your heart’s content!

Features: Cheap Rates – While Skype offers low rates on international calls, Vonage’s rates are 30% lower than Skype’s across the board. Don’t forget that all calls to the U.S., Canada, and Puerto Rico are also free for a limited time.

Integrated Address Book – Instead of having to manually enter in phone numbers/screen names in Skype, Vonage Mobile just uses your phone’s existing contacts, allowing you to check which of your contacts already has the Vonage Mobile app for free calls/texts. You can also quickly send invites to whomever you want to get the app so you can both share in the free calling fun!

The Competition: As mentioned above, there are two heavyweights in this category:

Skype – Free – iOS 4.0 or later, Android 2.1 or later – Download it here for iOS and here for Android

Google Voice – Free – iOS 4.0 or later, Android 2.1 or later – Download it here for iOS and here for Android

Why the Featured App is Best:  Skype is still indispensable for free video calls, but Vonage Mobile tops it when it comes to 1) cheaper rates and 2) much better address book integration. Meanwhile, Vonage Mobile outdoes Google Voice with free calls/texts between fellow app users, along with a dead-simple way to invite friends to download the app.

Summary: Though it’s not the end-all be-all in VOIP apps, Vonage Mobile has some very strong features that make it better than Skype/Google Voice in some respects. While it doesn’t replace those two great apps, it’s definitely worth a download as a free calling app whenever you want to avoid using your minutes.

What do you think of Vonage Mobile? Let us know in the comments!