Tap in using your own phone: Listen to other people's calls through your own basic telephone by hooking up your phone to a part of the original line that runs outside the house of your target. By cutting one of the plugs so that the red and green wires are exposed, you can figure out which part to plug into your phone and complete the connection.
Disable the microphone: Remember to disable the microphone on your phone or tapping device so you don't have to worry about making any breathing noises which will give you away.
Use a recording device: Voice-activated recorders are easy to install if you only want to hear short conversations, because the tape inside the recorder will eventually run out. These recorders can be hooked up to the original telephone and hidden under a bed or even inside the bed frame or under the mattress.
Install a bug: One of the most popular wiretapping devices depicted in movies and TV shows is the bug. By installing a bug into the receiver of a telephone, you can route the electrical current which airs the phone conversation to a radio transmitter.
FM wiretapping: This system relies on an FM frequency to send a phone call to your transmitter or listening station.
Record a call from your phone: If your wiretapping mission involves recording a conversation between you and your target, you can simply record the call. All you have to do is dial an 800 number, such as the one provided by RecordMyCalls.com, and the number of the person or company with whom you want to record a conversation. The service is marketed toward businesses, salesmen and attorneys, but you can technically (but illegally) use it however you want.