The function of the private line eliminates the possibility of someone other than you reviewing your call details, from phone sets, which have the shared extension, additionally no one can monitor your call or connect to you call.
The telephone number that is attached to a country, by dialing which it is necessary to take into account the code of the country or region you are calling to. When dialing the number from the same country you are calling to there is no need to enter the country code, but simply a phone number, sometimes a code of the region, might be a case when calling from one state or region to another, applicable to large counties (USA, Canada, Russia, China etc.).