A new Skype for the Apple iPhone app was just approved and is available in the iTunes app store called Incoming! for Skype. Basically, it makes every call an incoming call so you can save your minutes on your wireless dialplan, since they often feature unlimited inbound minutes and only charge for outbound minute usage.
Here's how it works:
1. Open the Incoming! App on your iPhone
2. Dial the phone number, choose from Favorites, choose from address book or conference call
3. Press call and it will re-route the call through the Skype helper app on your home computer.
4. Your phone then rings, you pick it up and then the other person is called.
Using this app you can connect to any landline or mobile phone over Edge, 3G, and WiFi - unlike the 'official' Skype for iPhone app, which is WiFi restricted - unless you jailbreak your iPhone for 3G support of course!
Basically the calls are routed through your home PC's Skype software. You will use SkypeOut credits for PSTN calls. But if you've already signed up for one of Skype's unlimited call plans (U.S./Canada $2.95/month), the call is essentially free. Another benefit is that you get some of the Skype features in this application. For instance, you can do 9-way conference calling on your iPhone, making business meetings while on the go a snap! 
Essentially, the app is harnessing the power of your PC for the audio mixing. (Note: I don't believe the free 'official' Skype for iPhone app can do 9-way conferencing)Features include a visual favorites list, address book and support for both Windows and the Mac. An iPod touch will work as well, but you can't route calls to it, but you can route it to a nearby phone.
The app will cost you $4.99 on the iTunes store, which is pricier than most iPhone apps.
You can check it out here
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Is the helper app on the PC part of the standard Skype install or a special that comes with this iPhone app?