Are you looking for a way of communicating with each other while you're traveling or for calling home?
As far as the cost and effectiveness of your phones in Europe, probably the easiest way to settle that is to call your cell phone company and ask them the deal. They might not be the right band for Europe, or you might have to pay roaming charges...there are so many plans out there, that it's really best to get the specifics from your own company so you don't get a nasty shock when you get home.
Calling cards work pretty well, in our experience. My mother-in-law gave us a rechargeable one from Sam's Club about three years ago when we moved to Lithuania., which we used for two years, and still use when we're traveling (we finally got a better deal on our phone bills when we moved to Germany.) You can add minutes over the internet, so if you get a 100 minute card to begin with (I don't know how long you are going to be traveling, or how often you will be calling home, or how long you will be talking each time), if you use it up you can just pay for additional minutes as necessary. And since you can use the cards stateside, I don't think there's any concern about left over minutes. These are also the kind of things parents love to buy before their children take trips, so if someone asks if there's anything you'd like or need for your trip, this might be a good suggestion.
For communicating while you're travelling, if your phones work, you could SMS each other, which would be a lot cheaper than calling, or for our last trip we used little walkie talkies. They worked okay, but the batteries ran down fast, it seemed to me.