It's a common problem: you have contact information for a person or company abroad, but you don't know how to call it from your iPhone. Here's how to do it.
First you want to check your mobile subscription for international service. Some mobile phone subscriptions do not contain international calling. If that is the case, consider buying a prepaid international calling card from a supplier such as Amazon.com.
Some telephone subscriptions may also charge a fee for international calls. Make sure you know all the possible costs before you call.
When you are ready to make a call, unlock your iPhone and launch the phone app.
 Tap the Keyboard button to switch to the keyboard mode.
Tap and hold your finger on the "0" key.
While holding your finger on the zero key, the 0 in the dialing area changes to a plus sign ("+" ). 
Enter the telephone number on the keypad (starting with the country code) and then press the green call button.
International telephone numbers contain an area code (just like an area code) that tells the telephone system how to handle the c all. Each country gets its own unique code (such as "49" for Germany, as shown in the example here), and this is usually the first digit or group of digits at the beginning of the telephone number.
The call is now placed. Speak as usual on the iPhone and enjoy your call!