If you want to be able to recognise an international call coming into your phone, you need to be familiar with how international calls are placed. An international caller first dials an international access code to dial out of their country, then they dial the country code for the United States. Likewise, if you were to dial another country, you would dial an international access code and a country code for the place you are calling. Knowing these two pieces of information help you to recognise international calls on your phone.
Look at the first few digits of the incoming call. If the number begins with "011," the call is an international call; "011" is the international access code for the United States.
Look at the next two or three digits of the code. This code indicates which country the caller is calling from. For example, "93" is Afghanistan and "44" is the United Kingdom.
Look at the remainder of the number. This is the person's telephone number.
If the number shows as "unavailable," it means that your telephone company cannot trace the number: most likely because they have not subscribed to a database that accesses the numbers. Therefore, "unavailable" could mean either a domestic or an international call: You have no way of knowing until you pick up the phone.