First of all, I could be off my rocker and under caffeinated. But I THOUGHT that if you were in a call and someone called in, the second line on a Yealink T46 would indicate that a second call is coming in (call waiting is enabled on the test phone). However, the second calls are going straight to voicemail. I did upgrade to 15.5 two days ago, but I can't confidently say it was working before then. Any thoughts on this?