Mobile/GSM area codes always begin with 04xx and the subscriber number is six digits long. Numbers are usually provided by Mobistar, Base, or Proximus. Each provider has a unique number assigned as the second digit in the area code: Proximus numbers begin with 047x , Base numbers with 048x and Mobistar numbers with 049x . With the introduction of number portability, area codes may no longer correspond with their providers.