The calls have excellent sound quality and are highly secure with end-to-end encryption. You don't even need to configure your firewall or router or any other networking gear.
Additionally it doesn't just work on Windows. Skype is also for Mac OS X, Linux and PDAs using Pocket PC, with a native look and feel for each platform. Talking, sending instant messages or even file transfers work between different platforms like a charm.Skype calling - Skype has all the features of an ordinary phone so it's even easier to manage your calls.Video calling - see who you are talking to at the same time as speaking to them.Add Skype and SkypeOut contacts - Add contacts who use Skype and those who use ordinary phones so you can call more people.Organising groups - group contacts under certain names and share them with your contacts so they can talk to them too.Basic chat and emoticons - when it's not convenient to call, chat or Instant Message (IM) your contacts.Group chat - for when it's easier to chat or Instant Message (IM) all your friends at once.Profile settings - change how you appear to the world and let people know a bit about you.Conference calling - talk to more than one friend at a time.Import contacts - search your address book to find friends and family that already have a Skype name and start calling them for free.View Outlook contacts - view and call your Microsoft Outlook® contacts quickly and directly from your Skype contact list.Quickfilter and Speed-Dial - find Skype contacts, recent chats and SkypeOut contacts quickly and easily, then enter their Skype name to call them back quickly.