What is a PAC?

A PAC is a Portable Authorisation Code.

This is a unique identifier assigned to each mobile phone contract which allows customers to easily change mobile phone carrier. The PAC is available on the telephone invoice or on the account management interface but can also be obtained by dialling 7777 from the mobile whose PAC is to be obtained, or 0333 003 7777 from any other phone. A voice server then communicates the portability authorisation code, by voice but also by SMS. 

This service can be accessed 7 days a week, 24 hours a day. The call is usually free.

A PAC consists of a series of twelve digits which define the identity of the operator but also qualify the customer - professional or private - as well as the nature of the contract.

The series of digits goes as follows: OO (operator identifier code), Q (quality of the customer: professional or private), RRRRRR (contract number), CCC (control code).

Check this article to learn more about portability.