Recently received Marshmallow update including option for wifi calling.Wifi calling is only turned on when cellular signal is super weak or not available at all. I was able to "force" the wifi calling on at home with airplane mode and then turning wifi back on.That is desirable as my signal at home and office varies quite a bit and wifi calling allows consistent service. Now today at our office, I can't use phone in airplane mode with wifi turned on.It shows a message "turn off airplane mode to make call". Other people with Iphones seem to be able to accomplish wifi calling in airplane mode in this same location (office). Any assistance or insight would be appreciated. Thanks