There are several ways to handle unwanted phone calls. Residents of the United States can register their telephone numbers with the Do-Not-Call Registry. Another way is to block calls or ask the phone company to set up a call tracing system.
The Federal Communications Commission has put in place, alongside the Federal Trade Commission, a national Do-Not-Call Registry. Telephone numbers can be registered with them, free of charge, by telephoning the registry at (888) 382-1222, or alternatively, contacting them online at www.donotcall.gov. Telemarketers are not allowed to call a number if it is on the registry, thus reducing the amount of unsolicited calls.
Calls can be blocked on a mobile phone by using applications such as Call Bliss for iPhone or Call Control for Android. These applications ensure that individuals can receive calls from those they wish to hear from and those they don't cannot contact them.
For call tracing or call screening set up via the local phone company, the information collected is passed directly to law enforcement officers who will then attempt to put a stop to the unwanted calls. The most simple method, of course, is just to hang up.