These codes we are talking about is categorized into three; below are them
These codes are hidden codes that you enter on your phone that contain the asterisk (*) and the hash (#) signs.
Once you dial the codes your devices will automatically communicate with the computers of the provider.
The Man Machine Interface (MMI) are numbers entered on the dial pad which activate the local hidden device menus.
There might be no communication with the provider’s computers when you dial these codes.
You can see the pronunciation of this ones are not really serious, ‘Supplementary’ (Supplementary Service codes).
So therefore their uses are not really important like that, they include codes which are a mixture of the two previous ones.
When you dial these codes on your computer, they either activate hidden feature or send requests to the service providers even without communicating to remote computers.
Click Here for the complete list of the codes