When the phone is off (battery dead) or in airplane mode, any calls instantly go to voicemail.
I use call forwarding from Xfinity Connect (it wouldn't matter which service is used) to get calls to my home phone forwarded to my mobile number AND my wife's number so we can pick up on calls when we're not at home.
The problem is that if one of the mobile numbers is "offline," then the call instantly goes to that phone's voicemail and there is no opportunity to pick up on the call at the original (home) phone or the other mobile phone.
So, what's needed is an option to NOT transfer to voicemail when the phone is "offline" before the number of rings that have been set.