Vonage is gunning for the mobile VoIP market in a big way with its new Vonage Mobile app for iOS and Android, which it says offers calls that are typically 30 percent cheaper than Skype's rates, based on per-minute rates to the top 50 countries called. You don't need to be an existing subscriber to use the service, with prepaid credit being used to pay for calls. App to app calling is totally free, and the company says these use a high-definition audio codec which offers improved audio quality over traditional voice calls on cellphone networks, though it doesn't list a minimum bandwidth requirement beyond 3G. As a nice touch, both Android and iOS versions offer in-app billing, using your iTunes or Android Market account to add $4.99 or $9.99 credit packs so that you don't need to give Vonage your credit card details. Besides the cheaper calling, Vonage is offering users free calls to phones in the USA & Canada for a limited time.

The app is able to use your mobile number — verified via SMS — so that your caller ID shows up correctly for outgoing calls, and will also offer your phone's address book for easy access. This isn't Vonage's first foray into mobile apps — the company has an "Extensions" app for its home phone users which allows them to use their international calls anywhere — but providing users with its full-fledged service is a big step towards competing with the likes of Skype and Google Voice.

Update: Vonage tells us that the minimum bandwidth required by the app is 64KBps — impressive if the audio quality can be maintained at such a low data rate.