A while back, I got an Obihai box, connected it to VoIP.ms, and I've been happily ever after paying $5-6/month for all the phone service I could ever want. (2017 thread.) So far so good, but can it get better?

I've been contemplating replacing my office desk phone (cheap, single line, analog phone) with something snazzier that can play more interesting games with VoIP.ms like conference calling, or connecting to an external headset for those interminable multi-hour phone meetings. So far as I can tell, a wide variety of SIP devices are completely compatible with VoIP.ms, including several models in the $40-50 range, and then you can get a variety of standard accessories like EHS headsets (which can pick up and hang up the call without you needing to press buttons on your phone).

But there's one thing that seems to be evading me -- when you answer the phone and it's for somebody else in the house. Traditionally, you holler out "Hey, sweetie, it's for you!" You wait for them to pick up, then you hang up. Easy, right? So how does that work in the VoIP universe, when you've got multiple independent devices logged in to receive inbound calls from the same phone number? Once one of them picks up, the others go back to idle. You pick up a second phone and it's going to give you a dial tone.

So... is there some way to make multiple VoIP phones, connected to the same service at the same phone number, behave like old-school POTS phones in letting you share the call? Is there even a technical name for this sort of thing?