Check out Jmp.chat

It’s not directly what you’re looking for, but it does offer VOIP via XMPP. Voice calls are crazy cheap, like 0.1¢/min, or something (I forget, it’s so silly cheap I just don’t care).

You can use it stand-alone, or port your phone number in and now everything (calls/sms) go through XMPP. This is how I found them, as a solution to crappy SMS being tied to a physical device. Now my (crappy) SMS is on any XMPP client I use - phone, laptop, desktop, iPad, etc. And all calls are VOIP from any device, so long as the client supports it. I don’t think there’s a Windows client that yet supports voice (Gajim is the go-to for XMPP on Windows), but there’s: Android (Cheogram), Linux (Gajim) and iOS (Snikket).

Er, is it when rain travels down spider webs?

Got a link to what you’re referring to?

But that approach you lose wifi.

Though I have 3 laptops with both wifi and cell, 2 old Dells and a newer Lenovo.

I think the complaint here is Apple not even giving the option of both simultaneously.