The Make Set Busy feature in CS 1000 had the following functionality:

The Make Set Busy (MSB) feature allows a Meridian 1 proprietary telephone to appear busy to all incoming calls. Outgoing calls can still be made from the telephone. To activate this feature, a separate MSB key or lamp pair must be assigned. Incoming calls to Multiple Appearance Directory Numbers (MADNs) in the MSB mode are still signified by the indicator next to the Directory Number (DN) key and can be answered even while MSB is active. Calls to any Single Appearance Directory Number on the telephone receive a busy indication.

In the details, the MSB feature provides coverage treatment. For example, if a call to the station result in redirection to voicemail, if MSB was active, the call will automatically be redirected to voicemail.

The MSB feature corresponds to the Send All Calls feature and button on the Communication Manager system. The Send All Calls button is configured as using a coverage path to provide the desired capability.