Well, no and maybe yes...It is true that the normal voltage in telephone wires, which provides the dial tone, is not dangerous. In the U.S.,it is around 40 volts DC, with low amperage. Amperage provides the "push" to electricity. A good example of high voltage, low amperage is the static charge you get shuffling across a nylon carpet and then touching a doorknob or somebody's nose. The charge is on the surface of the skin, and doesn't have the "push" to penetrate into the body.
However, when the phone rings, a series of high voltage AC surges come through the lines, up to 100 volts, and this can be dangerous, especially to people with health conditions, pacemakers, etc. And unless the phone company thinks your phone is busy, it will do its ringing thing, even if your phone is unplugged!!
So disabling the line is simple- just take one phone of the hook, and wait for the phone company to finish its off-the-hook warning tirade. Then proceed with your work....