Skype lets you make free phone calls through the Internet, but only if you're connected to a Wi-Fi network. (Skype can't make free calls through your cellular phone network.) To use Skype, you need to create a Skype account (http://www.skype.com/). Creating an account involves defining a username and password.
You can also use Skype to call mobile or landline phone numbers. The only difference is that when you call a non-Skype number, you need to pay per minute.
After you tap Skype from the Home screen, you'll see five icons at the bottom of the screen:
Contacts Displays a saved list of phone numbers and usernames
Chats Displays any incoming or outgoing instant messages
Call Lets you type a phone number or Skype username to make a call ...