The Mobiola Headset app for the iPhone offers simple and easy option to record VoIP calls. It turns your iPhone into a mobile headset for your desktop PC, too.
The app's idea is pretty simple: Your iPhone becomes a mobile headset (and recorder) for VoIP calls made on your Mac or PC. The way it works is that you download the Mobiola Headset app on your iPhone and Mobiola's desktop application on your desktop and connect both devices to the same Wi-Fi network to link up. Then fire up a Skype call and hit the big red record-o button on the app (well, warn the caller you're recording them, too) and voila, you'll get saved audio files of your call. It's dead easy.