I've done well with Pin cards that are for one country only (as opposed to multi-country pin cards). I usually get a 5 Euro card. If it doesn't work or I don't use it up, I'm not out much.
There will be places that sell them in the Airport (and the phones will probably work there too), look for a store that sells newspapers and/or tobacco. When you buy the card, ask the person who sells it where a phone is that takes the card. They will point to a nearby phone.
While you are on that phone, try to notice some logo on the phone that matches a logo on your card. Not all cards work in all phones (and many phones don't work at all). It's less embarassing and time-consuming later if you figure out what to look for early.
Some people suggest getting a calling card at Costco. It may be a good idea but I haven't tried it yet.