All phones must have a way of making and then terminating a connection to the phone network; however the exact procedure for doing so depends upon the nature of the phone (e.g. landline, cell phone, satellite phone). Write a abstract class, Phone, that contains a string instance variable, phoneNumber, a constructor that accepts a string parameter initializing the instance variable, an accessor method, getPhoneNumber, that returns the phoneNumber, a toString method that return the phoneNumber in the form