Here's a short take on a simple Windows Phone app that will help you with international dialing. Call the World is a dialing app that will add the country dialing codes when you make calls or texts while traveling abroad.
Call the World is laid out fairly simple. You have a drop down menu to choose the country you are calling and the "+" extension is displayed in front of the dialing field. Call the World currently supports (automatically inserts the code) France, Germany, Spain, U.S. and the U.K. One would hope that more country codes will be added with future updates but in the meantime you can manually add the codes in the prefix field that aren't covered automatically.
You can enter the phone number manually or tap the "Look Up" button to select the number from your contacts. At the bottom of the screen are two buttons to toggle between using the app for phone calls and sending text messages.
It's a simple Windows Phone app that could come in handy for quickly adding country codes. The alternative is to manually add the codes in your contacts when you travel. Call the World is a free app that you can grab here at the Windows Phone Marketplace.