Call handling is simple. I have two telephone numbers and 1 SIP number. The primary phone number is +1 412 253 2956 which is a Google Fi telephone number. Calls to that number will ring my cellular phone at anytime. In addition, any outgoing calls will display this number as the only phone line is my Google Fi service.
My second number is an iNUM telephone number which a non-geographical telephone number. While support for this number is spotty, it is a standard ITU telephone number which should be supported. This number will ring my cellular phone and will either use data services, or forward to my cellular phone number. This telephone number is +883 5100 0999 0651. Calls from supported companies will likely not charge for calls.