To ensure that Star Codes work as described, you may need to disable any local Feature Codes on your device. For example, on a Grandstream handset, on web user interface, go to Feature Codes menu and select No for
Enable Local Call FeaturesCall Forward All Calls (
*71 / *72)Call Forward on Busy (
*73 / *74)Call Forward on No Answer (
*75 / *76)Do Not Disturb (
*78)