Answer:
Yes, Skype is available on the iPhone, the iPod Touch, and the iPad.
Since there is a Skype application for the iPhone and the iPod Touch - and ALL applications from the above can run on the iPad - you can install the Skype app on the iPad. There is a built-in microphone so you can call straight from your iPad!
On Apple devices (e.g., the iPhone, or the iPod Touch) there is an "App Store" where you can buy apps, include the Skype app.