Why does my phone give me a connection problem or invalid MMI code comes up when I try to make a call?

[AC Question]

connection problem or invalid MMI code comes up when I try to make a call help

Please can someone help

 

[B. Diddy]

Re: connection problem or invalid MMI code comes up when I try to make a call help

Welcome to Android Central! Which phone? Have you spoken to your carrier? Did you buy the phone new or used? Check the IMEI to make sure it hasn't been blacklisted: ESN / IMEI / MEID Check (Free) > Swappa