MMI, or "Man-Machine Interface," refers to the numbers or text entered into your phone to perform specific actions. MMI codes typically start with an asterisk and end with the pound symbol. The symbols at the beginning and ending of the code prevent the phone from interpreting the code information entered as a phone number to dial and call. If you're on a call, you cannot access MMI codes. Many of these codes are programmed into your phone by the phone company. Your user manual will define those for you.
Invalid MMI Codes
If you input an incorrect code on your phone for a certain feature (such as call forwarding,) you'll receive an "Invalid MMI Code." You may also receive an "Invalid MMI Code" message after entering correct if you haven't subscribed to the service or feature with your carrier. For instance, some companies offer call forwarding as a standard feature, while others require that you pay extra for the service. If your phone supports user creation of these codes, verify that the information entered for the code is correct and that you are eligible for the feature or service.
Accessing Voice Mail and Features
The company with whom you have your service usually provides a series of numbers or text associated with the MMI codes already programmed into your phone. Included codes could include those for accessing voice mail or information on your phone plan, such as available minutes or payment options. If you enter a code designated provided by your phone company and receive the "invalid MMI code" message, contact your phone company for further information.
Sometimes, you can find out what software version your phone is running using an MMI code. You can access this information by inputting the code assigned by your phone company. If the company has changed the number or access to the information, you will receive an "invalid MMI code" error. If this happens, ensure that you entered the code correctly first before contacting your wireless phone carrier.
Corrupt SIM Cards
If you receive an invalid MMI code message and have verified that you entered the code correctly and are eligible for the feature or service, the Subscriber Identification Module card, or SIM, may be corrupt. If this is the case, your can carrier replace the SIM card for you. If you suspect you have a bad SIM, take the phone to your carrier's local retail outlet and ask them to check the module. Alternatively, contact your carrier by email or phone and ask that a new card be sent to you.