The homes, around the Great Leighs, Great and Little Waltham and Fairstead areas, have been cut off since Tuesday.
Emma Littlejohn, spokeswoman for BT, confirmed the phone lines had been taken from near The Crescent, Little Leighs, and contain valuable copper.
Copper has a high scrap value in the global market at the moment due to demand from the world's growing economies such as China and India.
Miss Littlejohn said: "We are doing our best to restore service and some people should be back on over the weekend.
"However there may be some disruption until next week."
The theft is believed to have taken place on Tuesday evening and anyone who saw anything suspicious should call police in Chelmsford on 0300 3334444.