I read on this site that BroadVoice, when connected as a VOIP line, has to be used thru Axon. They said BroadVoice made changes that caused problems with IVM.
While doing some packet sniffing I found that after turning off IVM it still "technically" answered the line. IVM didn't pick up because I had turned it off but it interfered with a software voice recorder that I ran at the same time.
I run my BroadVoice line through a Sipura PAP2T before it uses IVM.