You need to save the number with the international dialling prefix then the country code, area code and then the phone number. For example my cell number is 0419 xxx xxx and I am in Australia. The leading zero is dropped. The iPhone selects the international code for your country automatically by using "+". So you could use +61419 xxx xxx if you wanted to call me. Australia's country code is 61. If it is a land line you are calling, number would be +617 xxxxxxxx.
My area code is 07 and once again drop the leading zero.