VERIFIED SOLUTION i

Adding or changing your dialing prefix on the DM300C-DM475

Products affected: DM300C™, DM400C™, DM450C™, DM475™
A dialing prefix, such as '9', may be required to connect to an outside line, depending on your phone system configuration. Follow these steps to change your dialing prefix:
  1. Press Menu.
  2. Press Page Down twice.
  3. Select Data Center Options.
  4. Select Phone Settings.
  5. Select Dialing Prefix.
  6. Enter the required prefix and select Accept.
  7. Press Home to return to the home screen.
UPDATED:  March 12, 2019