Actually you can with T-Mobile's DIGITS program. I've been using it for over a year and when one phone rings, so does the other. It doesn't cost me anything for this either! You sign up, tell them the number you want to clone and T-Mobile sends you a sim card to use in the 2nd phone.
If you must stay on Verizon with their crappy customer service....you are out of luck as T-Mobile is the only carrier offering this type of service (as far as I can tell).