I think it's too much of a coincidence that it switched to the Macro network as soon as the call connected, though. I guess it just didn't seem like a "handoff" in the video, it just "switched" before the call began.
I just went outside and started a call on wifi, then walked away from the wifi while talking to someone. It became spotty and eventually I got the Call Failed message. No handoff.
iPhone 5C, Sprint 25.0 Carrier, iOS 10.0.1.
Has anyone else tried this type of scenario yet? This seems like the most common situation, like receiving a call in the garage on wifi, then driving away from the house.