Wow, I'm having the same problem, regardless if it's from a verizon user or not. I am also using Handcent. My daughter and hubby both have the Incredible but I only got duplicates from hubby that had the call back number. My daughter has her CB# disabled so I had hubby disable his and now I'm only getting one msg from him.....I don't know why that's the problem cuz It shouldn't matter as long as I have all my notifications on the stock messaging app disabled.
So just a heads up, as long as the person that's texting you has CB# enabled you'll get duplicate msg's....I hope this prob gets fixed, I don't want to ask everyone that texts me to disable their CB#.