1. My cell phone isn't working. - This is used for when your cell phone isn't functioning. It is a very general statement. It can refer to a big or a small problem of any type. 2. There's no service or signal. - This is something you can say after #1 to add more information about the problem. It's a very explicit phrase - it means that you can't call anybody. 3. It's broken. - This is very similar to #1, but is usually reserved for more serious issues such as your screen being cracked or the phone not working due to it getting run over by a car. It refers to a more complete loss of function. I hope this helps you.