notify
Invoked when there is a change in the voicemail counter for a specific call group.
This method is invoked when the count of voicemails is updated, either for a specific CallGroup or for all groups if callGroup is null. The provided counter parameter represents the updated voicemail count. You can use this information to take appropriate actions, such as displaying notifications.
Note: This method is triggered only when the application is active and running.
Parameters
call
The CallGroup instance representing the specific group, or null if retrieving the total voicemail count for all groups.
counter
The updated count of voicemails, representing the total count for all groups.