Anonymous, blocked, restricted, and private calls can be frustrating. Not only is it nearly impossible to screen calls from such numbers, it makes it difficult to catch harassers and telemarketers. While some people block their numbers to maintain their own privacy as opposed to acting maliciously, many people have experienced late night, vulgar, or obscene calls from private numbers. Telemarketers who use blocked numbers often do so because they have obtained someone's number illegally or through a purchased list. Fortunately, there are ways to figure out who private callers are, or block them from calling you altogether.
Dial 69 after picking up the private call if the caller hangs up. Dialling this code will typically call back the number that just called you. If 69 does not work, you can also try the following codes: 57, 67, and *71.
Contact your phone company and ask if a call tracing service available. This allows the phone company to see the number of a private caller, although the number won't be released to you. When the person calls, you will simply pick up the phone and enter a code to record the number. This is especially useful if the private calls are consistent or harassing, because your phone company can then give law enforcement the number of the person calling you. Some phone companies charge for this service, so be sure to inquire whether there are any fees.
Sign up for a service such as TrapCall. These services will figure out blocked numbers and private callers and then send the revealed number to your phone. This type of service only works for mobile phone users, and cost from £1.90 to £16 per month, depending on the features you choose.
Subscribe to Anonymous Call Rejection (ACR) by contacting your phone company. ACR will automatically block private calls so that you won't receive them--you'll no longer have to even hear the phone ring when it's a caller from a blocked number. Although ACR does not work when the private caller is using a pay phone, many phone service providers offer this feature free of charge.
Call your phone company to see if Privacy Manager is available to you. This service will make it so that private callers must unblock their number, enter a code to reveal their number, or record their name in order for the call to ring through to you. When the call does ring through, you'll be given the option to accept or reject it.