skype

The same way you would use it to call someone in the US. All you need is an internet connection.

I know this isn't a direct answer to your question but have you scrolled down to see this same topic discussed about two days ago?

Practice in the US, then do exactly the same in Europe. Use the devices you are traveling with. Easy.

We used Skype last month to call the US from the UK on an iPad. To call a landline or mobile phone (not another Skype number) I believe you will need an account with some money in it. I was very inexpensive, just a few cents a minute. It worked great except we weren't able to hear each other when calling from one hotel where the wifi signal was weak.

Skype is just another way of phoning, right? I gave up phoning years ago, not because of the cost (because I have a prepaid phone card), not because I couldn't find a phone (I see them everywhere), but because, with the time difference I could never find a time when I wanted to call and they wanted to listen. Now I use email, exclusively. It's so much more convenient - I post email when I have time; they post a response when they have time. Of course I also have a blog (website, actually) where I upload a detail account for everyone over here to read any time.