SkypeOut, the opposite of SkypeIn, lets you call mobile and landline phones using the Skype application on your computer or smartphone. This comes handy when you want to contact a person that is not using Skype. You will pay for your calls with Skype Credit or, if you call a lot, you could save even more money with a subscription.
You can check out the current Skype rates at : http://www.skype.com/en/rates/ and you can buy Skype Credits here. If you are a Nigerian, you can buy Skype credit using your GTB Naira Mastercard. I use the card to pay for my Skype USA Number subscription.
Remember, Skype to Skype Call is FREE!
I hope to compare Skype Out vs Viber Out rates later.