I haven't experienced this but it is not surprising to me. I have 2 microcell towers in my home that operate through wifi and when I am on a phone call on my iPhone and then walk to another part of the house where the signal hands off to the other cell tower, my phone call gets dropped. The instructions for the cell towers say this is normal. So, it is not a surprise that when you are on a phone call through bluetooth and then walk out of range of your phone to wifi, the call will drop. So, you either should make the call on bluetooth and stay in that range or make the call from wifi and stay in that range. In short, your issue probably isn't an issue but a normal consequence of switching between signals.