New WiFi icon appeared on my S5

[AC Question]

Hi, I've suddenly got a new WiFi type icon appeared on my S5 next to my normal WiFi icon. It's very similar, but is like and upturned phone receiver with the semi circular WiFi coming from it.
I'm connected to my BT Homehub, and it's showing the data as coming to and from it, but the bars on the other icon are solid. Has anyone experienced this with BT, and can tell me what it means/how to switch it off?

 

[hallux]

Considering it has an upturned phone next to it, I presume it would be WiFi calling. Some say it can be turned off, it might have even been mentioned in a front page article here or on the GS6 sub-forum.