Egypt's three mobile phone companies will activate an additional digit that will be added to phone numbers as of Thursday.
The new numbers will be comprised of 11 digits instead of 10.
In a statement on Tuesday, the Telecommunications Regulatory Authority (TRA) said the service could be affected for up to three hours while the change is being made.
The companies launched campaigns explaining how to automatically apply the new system to phone contacts.
When dialing a number, subscribers will hear a recorded message to notify them that the number has been modified, but the call will still go through.
The TRA gave a grace period of four months for operating the old numbers.
Translated from the Arabic Edition