I think this cab is causing problems for you because it is designed to work with GSM phones. If you have a cdma phone it and your phone is connected to internet and a call comes in, it just flips out. I tried to tweak around the registries a while ago but it doesn't seem to work. So you can either have your internet shut off but unable to answer calls when you're on data or be able to answer calls but no data auto shut off.
I'd love for someone to prove me wrong cause I've been looking for a similar solution too.