I have MagicJack VOIP and moved my POWERED cordless phone next to magicjack box and router in a back room. There’s a nearby phone jack that connects to the rest of the house and tried using that with an old school unpowered phone. It worked on the first try but then I couldn’t hang up without disconnecting the phone line.
A word of caution if you connect the Ooma box to a wall phone jack. Be sure that the phone line to the street in the outside phone box is disconnected. The line that comes into your house should have a box outside. If you open it up, you may see some typical phone jack plugs. There is a jumper cord that goes between the street jack and your house jack. Make sure that jumper cord is disconnected before plugging your Ooma into one of the wall phone jacks so you’re not sending a signal to the street.
However, it may be easier to just use regular cordless phones. Plug the base unit into the phone jack on the box and then distribute handsets where you need them.
I know you were asking about Ooma, but I’ve been using Phone Power for years. It’s been pretty reliable. In fact, it’s been so reliable that I forgot what company I was using since I hardly ever have to contact them. Their box comes with two phone ports:
You can plug a separate phone into each port. By default, both ports will have same phone number. They call it a cloned line. But you can pay a bit extra to have each port have its own phone number. They also have support for Virtual Numbers. That’s an external number that will ring to your primary line. However, if you call out, the caller id will be your primary number. I can’t say how well these additional number features work since I haven’t used them.
Another solution is to port the numbers to Google Voice. That is a web-based phone system. You can make/receive calls on the web or on your smartphone with the the Google Voice app.
And another solution is to use a phone parking service. These are services which host your number on their server. They can forward calls to a different number or take the call as voicemail and forward the recording of it to your email. If all you want is to not miss any calls going to these numbers, a number parking service may work for you.
For me, the Ooma is a “belt and suspenders” backup so that the Ottlets can reach me if I don’t have my mobile with me or am sleeping too soundly to hear it (like @Raza, I use a multi-handset cordless system, and the ringer would wake the proverbial dead). I shelled out for the “premium” package, which allowed me to set up a whitelist of numbers it will accept; anyone else is told to go away.
Faxing has been addressed, the only thing I have to add is that you have to use a prefix (*99) to tell the unit that it’s a fax call.
A caveat (at least for my unit): two RJ45 jacks means that you can put the unit in the middle of a string of devices. But it tops out at 100Mbps.
No offense intended, but “Ooma VOIP” sounds like the sound people make when upchucking a bad meal.
LOL, that’s a point. You can practically hear the, “URP!! SLOP!!” that follows. 
Same here. We’ve had Ooma for a few years and it works well but now it gets about one spam call a month. We won’t be renewing it when this year of the “plus” service expires. I’ll probably move the number to Google Voice just to keep the number which we’ve had for decades.
We’ve used Ooma for about 5 years and like it very much. The Ooma box is plugged into our router, and we have a wireless base station plugged into the Ooma box. Then we have extra phones scattered around the house that are synced with the base station. The Ooma voicemail, and voicemail notification options, are great.
This honestly looks like the perfect set up for me, too. Thanks for sharing all the information! I will look into Phone Power before making any final decisions. You also shared about some other good options I hadn’t considered because I had no need to know about them before now. I will investigate those, also.
@ratatoskK, that all sounds great. My set-up would be just the same, only with 2 base stations instead of just one. I’m glad you’ve been happy with Ooma. I love the clarity I’ve heard when talking to others who use it. That’s really important to me.
It’s been a while since my initial setup, but I believe there is an upper limit to how many devices you can have on the Ooma line.
tl;dr is that they give you a maximum REN (Ringer Equivalence Number) for the unit and you add up all the RENs of your individual phone devices. So long as you stay under the maximum value, you’re good.
I have Ooma and it works well enough. I’m not a big fan because my voice quality is not always as good as I’d like, but it works well enough.