Don't call the experts to check your phone lines. If you are the average person. If you're not involved in industrial espionage or government intrigue. If you suspect an acquaintance, neighbor, or even a family member of being the culprit. You stand a good chance of discovering the eavesdropping device yourself.
Basic wiretaps are just that - attachments to the telephone wires.
Most amateur taps can be found just by looking at the wiring. There is no need to touch. In fact, you should never touch or tamper with unfamiliar wiring, or wiring which does not belong to you. Know What You Are Looking At Household telephone wiring generally contains four pieces of wire in one cable. The cable is usually round.