You only need to buy minutes on your Skype account if you are calling a land line or a cell phone. If you are using Skype from an Iphone with wireless or from a laptop, and are calling another computer, Skype is free and you won't need to purchase any minutes.
I travel overseas for work and use Skype quite often and it works great. You can use it for free for Instant Messaging, Voice calls or video calls as long its from PC to PC or IPhone/Itouch to PC and you have wifi connected.
We used it on our last trip to CSS and brought a cheap, $15 web-cam so we could do video calls with the kids. We could connect to the wireless right from the room and it worked great.