Upload software onto a cell phone: Cell phone surveillance is a higher tech form of wiretapping, and it's even easier to do. Whenever you're around the person you want to spy on, take advantage of bathroom trips or any other circumstance that causes him or her to leave the room without his or her cell phone. You can quickly install a monitoring software program onto the phone which will record calls and text messages. If you're really devious, set up an alert so that you know when that person is on the line talking with someone with a number you're curious about.
Use a cell phone as a bug: The Web site GeeksAreSexy.net discusses the "advanced eavesdropping" technique of using a cell phone as a bug. The service FlexiSPY allows you to dial the cell phone number of the person you want to spy on, and you'll be able to hear all that's going on in the room. The best part is that the cell phone never rings or vibrates, so no one knows you're listening.
Track someone's whereabouts with their cell phone: Without needing to break into someone's house or steal their cell phone for a few minutes, you can use World-Tracker to find out a person's whereabouts. The service currently only works for phones registered with U.K. phone companies, but is easy to use. Just type in the target's number, and World-Tracker finds the phone for you on a map.
Wiretapping VoIP: Though it's much more difficult to listen in on a call made over the Internet, it can be done. VoIP operates by digitizing your voice into bits that are transmitted over the Internet and are reconfigured, but are never actually turned back into sound waves. VoIP also runs on your ISP, which is more open than regular phone lines. A product called Cain & Abel was designed to record VoIP calls by by decoding the bits and turning them into WAV files. Cain & Abel is available here.
Buy a kit from Toys "R" Us: If you're too lazy to come up with any of these constructions on your own, you can always buy this wiretapping kit from Toys "R" Us, which helps you build a dime-size wiretapping device that can "fit into most telephone handsets."