public GSM(string model, string manufacturer)
{
this.Model = model;
this.Manufacturer = manufacturer;
this.display = new Display();
this.battery = new Battery();
}
public GSM(String model, String manufacturer, Decimal? price, String owner, Battery battery, Display display)
{
this.Model = model;
this.Manufacturer = manufacturer;
this.Price = price;
this.Owner = owner;
this.display = display;
this.battery = battery;
}