Your Digital Voice service can support two calls at the same time.
Multi Call is a new feature for Digital Voice customers. If you have more than one Digital Home Phone connected to your Hub, two people can make separate outgoing calls at the same time. Or you can be on the phone and another incoming call can still get through and ring any of your other Digital Home Phones.
This is great for busy households who don't want to miss important calls. But if you'd rather stick to just one call at a time, you can change to this in the Settings menu, under Line settings.