A Cell phone tap usually refers to someone listening in to a cellular telephone conversation without the user's knowledge. Since cellular phone calls are wireless a physical tap would be impossible. Therefore the term cellular phone tap, in this case, is synonymous with cellular eavesdropping.There are many cellular telephone handsets that can be modified to be used as a room bug without the owners' knowledge. However to tap a cell phone requires very expensive computer equipment costing more than a $100,000 USD, which can track a call as it moves from cell to cell.