I hope to keep my existing Verizon contract but replace my current phone to take advantage of the 4G LTE service now available in my area. In looking at craigslist resales I see the statement "clean ESN for Verizon." Can you explain what that means, and is there anything to watch for in purchasing a used phone? In particular, how do I know that it will work on the Verizon network. Finally, if I decide to sell my existing Droid X, how do I "wipe it" so that data/info etc. is no longer on the phone. Thanks for your help.