Over 1,000 people get struck by lightning every year in the United States, and over 100 of them die as a result of the strike. Lightning is a very dangerous force that, yes, can even reach you indoors if you're in contact with the telephone or plumbing.
If lightning strikes the phone line outside your house, the strike will travel to every phone on the line -- and potentially to you if you are holding the phone. So, if you are indoors during a lightning storm, stay off the phone. If you must call someone, use a cordless or cell phone -- that way, you're not in contact with any wires that run outdoors.
Stay away from plumbing pipes like your bath tub or shower, as well. Lightning has the ability to strike a house or near a house and impart an electrical charge to the metal pipes used for plumbing. If you're touching those pipes or anything connected to those pipes, that electrical charge has a path to you. This threat is not as great as it used to be, because PVC (polyvinyl chloride) is often used for indoor plumbing these days. If you are not sure what your pipes are made of, wait it out.
And while you're at it, switch off your appliances and electronics before the storm hits. Such devices as your computer, television and air conditioner all provide potential pathways between the lightning and you.