Most of network providers around the world are not using country code for local usage, they use only network code for calls and messages locally, but sometimes this will bring you some problems in identification of callers, specially when you move to another country or change your network provider to those kinds of network providers which uses country code all the time. Here you will find How to add country code to iPhone contacts easily.
The problem comes when you go outside of country, you can not call your contacts which saved without country code, you will have to edit the contact and add a country code before making a call. Another problem is that you can not identify incoming calls while you are out of country and or changed to those kinds of carriers which uses country code all the time.
How to add country code to iPhone contacts
ّDownlod the app called; “Contacts Optimizer” Click here for Download
After installation, Open the app choose account to manage, and then click optimization wizard and follow the instructions.
Hope this help you