Cell phone ring problem

Now people use cell phone all the time, we can talk with people on the phone all of the time. But some places have too much noise, when people call us, we can not hear the phone ring, or some of places are very quite that the ring is too loud. So now we have one problem about the phone ring. Some times cell phone ring will make people very angry, like when you are in class, and suddenly your friend calls you about weekend plans; the ring is too loud. At that moment, your classmate and teacher will be very angry with you. Maybe you are on the way to your office, and it is very loud outside so you are worried about who will call you, you make the volume loud, but you forget turn off it when you arrive at the office. If your phone rings, a lot of people will be angry. Some cell phone’s rings are very loud, so in public places it will make people angry. We cannot control when your friends will call you, but we can control the phone ring volume, and give people a peaceful public place.