How to call from France:
All French numbers have 10 digits and begin with 0.

France is divided into 5 geographical zones corresponding to five separate telephone codes: 01(Paris and the Paris region), 02 (north-west France, Reunion Islands and Mayotte), 03 (north-east France), 04 (south-east France) and 05 (south-west France and the Atlantic Ocean overseas territories).

Mobile numbers start with 06 or 07.
 
How to call from abroad:
Dial the international code 00 followed by 33 for France, then the number without the first 0.

Example for a Paris number: 00 33 1 40 00 00 00.
 
How to call from France to another country:
Dial the international code 00, the code of the country, then the number without the first 0. Examples: 49 for Germany, 44 for UK, 39 for Italy, 34 for Spain, 11 (AT&T) or 19 (MCII) for US, 16 for Canada (0 800 99 30 16 AT&T Canada).
 
Mobiles:
Contact your mobile phone operator who will confirm whether or not your mobile is compatible with the French network and also explain how you will be charged for calls received from your own country or that you make while abroad (local and international calls).

Note: To connect to the Internet and send multimedia messages from your smartphone, you have to turn on data roaming (unless you are on a Wi-Fi network). Data roaming can be switched on from the network settings of your phone, but you may incur additional charges - be sure to charge what those charges are with your provider.

From June 2017, you do not have to pay additional roaming charges when travelling in any EU country. This means all EU citizens can use their mobile phone to make calls, send text messages and surf the Internet at no additional cost.

Connection with the French network:
Some mobiles from other countries don’t automatically connect with the French networks. All you need to do is choose the option "network selection” on your mobile to manually make the connection.

Adapter:
Don’t forget that you’ll probably need a plug adapter in order to be able to charge up your mobile phone.

Buying a local SIM:
You can also purchase a prepaid SIM card from a phone store to use the French cell phone network: this way you’ll know exactly how much you spend. You can buy a SIM at the Airport or Buy a prepaid package at a book store such as the Chain 'Relay'. Relay stores can also be found throughout Paris. 
 
Buying a prepaid sim card at Relay - Airport
The book stores at Paris Airport are called Relay and have big red signs with white letters. They are several around the airport. Terminal 1 and 3 have both one shop and there are 3 or 4 around in Terminal 2. Buying a prepaid sim card from Relay is not convenient at all, because no one can really explain you what packages are available. The employees are already too busy selling water, sandwiches, magazines, etc.
 
The Relay shop that sells a prepaid sim card for France in Terminal 1 is not located in the Arrivals Hall but at Departures floor 2 CDGVAL Airport Shuttle. Next to the Starbucks in Hall 5. In Terminal 2 and 4 the Relay shops are in the Arrivals Hall.  All the Relay shops sell an Orange sim card packages:
  • €40
  • 10GB - 4G network all over Europe
  • 120 minutes calling from anywhere in Europe to the world
  • 1000 text messages from anywhere in Europe to the world
  • Valid for 14 days
Or buy a SIM form an SFR shop in Paris
  • €35
  • 5GB - 4G network only in France
  • 60 minutes calling from France to the world
  • 1000 text messages from France to the world
  • 14 days valid
 
OR: Order online an 'Insidr SMARTPHONE' 
For a flat rate of ONLY 3euro per day you get 3Gb per day, 4G data connection, unlimited local calls and texts, a WiFi hotspot in your pocket. With your favorite apps one click away. Social media, navigation, communication and much more.
  1. Book and pay for your INSIDR service online with our secure platform using any credit card. You can also pay for your phone at the CDG Airport.
  2. Choose your pick up location: Paris CDG information desks, INSIDR office in Paris or receive your phone in a pickup point anywhere in Europe.
  3. Several ways to return your phone: From France and Europe via post or in person in our office in Paris.
Go to: https://insidr.co/insidr-smartphone/