You can, of course, just don't answer the phone unless the number of the caller is not listed in the phone book. From a particularly annoying caller to be saved, replacing the room phone. But, it is clear that such methods create a number of inconveniences.
Most of the major mobile operators, with greater or lesser degrees of enthusiasm offered to subscribers of the service "Black list" or "Black-and-white list to block the numberand unwanted callers. Function "Black list" blocks those the roomand that you feel unwanted. The function of the White list, by contrast, leaves available only the indicated numberand the rest will be blocked.
Another option: you can purchase a phone that has a built-in function is "Black list". Then you will not be spammed by calls from the phone neither bully nor my subscribers . Practice shows that it is better to rely on telephones than on services of cellular operators. At least when buying a new mobile is to ask the seller this feature, especially as many modern models fitted with it.
There is another way to protect yourself from annoying calls, it quite actively uses advanced youth. She shakes a variety of programs that protect subscribers from various mobile spam. For example, you can install on your cell phone programs like CallFilter or BlackListCaller that, after making the unwanted numberand will automatically drop calls.