The iPhone's service plans aren't the most expensive smart phone plans in the industry, but they're far from the cheapest.  But imagine if you could get one of America's hottest smart phones and get phone calls and ultra-low rates or even for free.  That's exactly what Skype for iPhone, recently announced is promising.

The new application allows Wi-Fi connected users to place free calls to fellow Skype users and call at reduced rates to traditional landlines.  The only downside is that cellular carriers have nixed mobile to mobile calling.

People that stand to save a lot with Skype are business travelers.  Typically when travelling overseas, many people run into compatibility problems with the local networks.  Even for providers with relatively good overseas coverage, like AT&T, the service providers typically hit customers with big fees.  With Skype, though, calls back home will remain the same -- either free, or really cheap.

As far as the interface goes, the new Skype iPhone app will strike PC Skype users as very different.  It’s much richer graphically and looks somewhat like Facebook in layout.  Users can put status messages, update a profile picture or even chat via different options in the Apps menus.  Chat is the only feature that you can use over cellular networks.

Skype has 400 million users and already has been released for Nokia, Windows Mobile, and Google Android smart phones, as well as Sony's PSP mobile gaming device.  A Blackberry version is coming in May.  It’s worth noting that the Android version allows 3G wireless-to-wireless Skype calls, unlike the new iPhone app version.  Also, all of the mobile versions still lack many of the features of their desktop brethren -- SMS, video and proper conference calling, file transfer, and voicemail. 

The iPhone app is available today for free to download on Apple's App Store.  It is also available for use with the iPod Touch, essentially making the Touch a potential phone.  Touch users, though, will have to buy a microphone to use the app.