There are several different ways to circumvent caller identification (ID), depending on where you live and why you want to prevent your phone number from being broadcast. Most phone companies let you block caller ID on a per call basis, on every call to a particular number, or on each call that is made from your phone line. In this case, you can block other phones from identifying you by pressing a specific button combination before you make a call. Other methods you can use to block caller ID include calling directly into a voicemail system, placing your call through an operator, or using a prepaid phone card. These methods may not technically block your phone from broadcasting your number, but they can prevent the person on the other end from knowing who has called.
Caller identification is a service that causes outgoing calls to transmit certain information whenever a call is placed. This information is typically transmitted while the call is set up or along with the ringing signal. In most cases, the information that is sent consists of the phone number of the line that originated the call, though some systems are also capable of displaying names. Caller ID can be used to screen calls and for other useful purposes, but it can also create privacy issues. In order to protect privacy, it is typically possible to block caller ID.
In the United States, phone companies are required by law to provide a simple and easy process for their customers to block caller ID on interstate calls. There are no similar laws governing intrastate calls, since the federal government lacks that authority, but most phone companies provide it anyway. If you want to block caller ID this way, you will need to contact your phone company to determine the correct button combination. In most cases, the button combination will consist of pressing the asterisk, or star key, and then two digits.
Most phone companies offer three different kinds of caller ID blocking. One type operates only during one call, and allows you to input a code followed by the number you want to dial. Your number will not appear on that person's caller ID during that particular conversation, but there is no lasting effect. A different code will typically let you block that number on all subsequent calls. The third type of blocking is typically activated by contacting the phone company, and will result in your information being withheld during future calls to all numbers.
There are also some other ways to prevent your information from being sent that do not involve traditional blocking. If you make a call through an operator, your phone number typically will not show up on a caller ID box. This same effect can also be accomplished by using a prepaid phone card. In some cases, you may also be able to call directly into a voicemail system, which can allow you to leave a message without your number showing up on the recipient's caller ID. This is typically accomplished by looking up the direct voicemail number for the phone company of the person you wish to contact.