OK, yesterday I bought a USB Wireless Network adapter for my desktop, and MagicJack for my phone. After a second evening of setting up, installing, configuring (you know the routine), I've got my DECT 6.0 phone and my desktop PC running off my car's wifi.
I discovered accidently that leaving the wifi on 24/7 is not a significant drain on the battery. The phone sounds fine, and while the PC's internet speed is noticeably lower than wired cable, it appears to be tolerable. Saying goodbye to telco and cable ISP represents more than $1,000 per year. Haven't done either yet. I'll take a while to evaluate.
Right now, my cable 'modem' is unpowered. It looks dead, poor thing.
EDIT: Oh, rats! One big CON: when the car isn't home, I won't be receiving any voice mail.
Or will I? Hmmm, I think MagicJack voice mail is stored on their server. I'll have to phone home tomorrow from work and see what happens.