I hadn't heard about the third-party phone-answering issue with ZVJ. If you try rooting and installing a custom ROM, I think you'll be glad you did. One of the nice things about rooting is that you can make Nandroid backups and Titanium backups, so you have a safety valve in case anything happens to your phone (including losing it).
Three nice things about installing Reborn ROM:
1) You get a lot more memory available for apps & data. I used to have to hassle with juggling installed apps because I'd get the "Low phone storage" warning. Not anymore. More apps installed. No warning.
2) You can uses Reborn's smart WiFi capability to automatically connect to WiFi when a trusted WiFi network is available, but automatically switch to 3G when no trusted WiFi network is available. Love that. WiFi saves battery life. It gives me a faster connection when available. I never touch it anymore.
3) You can set on-demand overclocking, which speeds up the phone when needed (at the expense of battery life) but slows it down when not needed (which helps battery life). Overall, it provides better battery life.