Gerry,
You are correct, if you were living in France you would have to use 0 before all phone numbers. In fact you would consider 0 as part of the phone number.
A trunk code is normally used for long distance calls. The US and Canada also use a trunk code – it is 1. When dialing state to state calls you must use 1 + area code + local number. In this case 1 is the US trunk or long distance code. There is a bit of confusion here since the US country code is also 1. So when dialing to the US from abroad you drop the trunk code (1) and dial the country code which is also 1.
One other thing: France has a so called closed dialing plan which means that there are no area codes or local numbers – all calls are dialed nationally using the national dialing format starting with 0.