Paying for SKYPE - Skype is free computer to computer. If you want to talk computer to landline phone, you pay, either on a cost basis or sign up for a year's contract which gives you "free" calls 24hr a day to all the phones in your chosen country.
SKYPE is a bit dodgy now and then (poor quality, noisy, echoes) but generally works well and is essential in countries like Spain where the phone lines tend to dissolve when it rains (i.e. all the time).