Answer by Japanese teacher
When you are calling out to a waiter in a restaurant to mean “excuse me”, you can use sumimasen. Sumimasen also means “sorry” and “thank you” (when you have troubled someone for his help). In fact, it is a three-in-one useful word that you must remember.
If you are lost and you want to call out to a stranger in the streets to ask for directions, you can add “anoo…” in front of sumimasen. Note that you have to hesitate and drag out the pronunciation of anoo slightly. Anoo does not have any meaning but it acts as a buffer to soften the shock of hearing someone say sumimasen out of the blue.
If you are entering a client’s office or other similar business situations and you want to say “excuse me”, we recommend using “shitsureeshimasu” instead of “sumimasen”.