Not enjoying the interruptions when someone arrives at your classroom door?
Set up a Welcoming Committee.
Two students each week are selected to do the job. Organise a roster for the whole term.
When someone knocks or comes in, the selected students quietly and calmly go to the door and say, “Welcome to our room, how can we help you?”
Unless the visitor needs to see you personally the Welcoming Committee deals with what ever is required.
If it is a class announcement the Welcoming Committee get the classes attention, take the notes to hand out later, or do what ever is required.
You as the teacher just continue on. Let the students do the job. Give them full responsibility. They are quite capable of dealing with what ever is required.
Students make decisions, sort out how to deliver the message with out interrupting the class unnecessarily, take on responsibilities and use effective communication and social skills.
The teacher continues on without having to stop the activity, the instructions, the teaching.