Have had it for a couple of years, the version that plugs into the USB port. Now they have a version that plugs into your router like the Vonage product.
The downside is that you have to have a computer designated to run the USB device. On top of that, you will need to regularly reboot the computer if you don't have static IP.
Been using MJ for about 2 years. I/We are very happy with it, on windows7, it works in sleep mode. You have to dial a 10 digit phone # to call out (always have to use area code even in your own area)Verizon is never going to get any more money from me for a land line.
I use one.
No problems with it although if you want your phone to ring when receiving incoming calls your computor must be on. If it's not on the call will go to your voice mail.
When you do turn off your computer and then reboot it will take about 5 minutes for MJ to come on line.
But for the price it can't be beat.
Another option is an Obihai device using Google Voice. I ported our landline number to GV (via a disposable cell phone) and we use this exclusively for our home number now.
A caution is that there is no native 911 service with GV, if you want that you have to add it via another service like Callcentric (abouit $2 a month). But so far the service has been flawless and mostly transparent to what we had.
There are two models, both exclusively available from Amazon. The less expensive one is $44 and the more expensive one is $50. What you get for $6 is a jack on the device that allows you to connect it to a landline for calls (in addition to those made via the Obihai device). If you have another line this is one more way to get 911 service. You can check it out on their website.
At this time it is free to the US and Canada (through 2011). Google may or may not extend that deadline. Also, it doesn't have to work with GV, you can use it with other services too. And mind you that this isn't a formal agreement to use GV with the Obihai - GV could change the API at any time.
Oh and another quirky thing (have I talked you out of it yet?) is that although caller ID works, it is only the number - not the name. Apparently a real telco subscribes to a number lookup directory, and that costs money. GV does not, so you only get the number being displayed. But at least that passes through. Our phones have an internal directory so as long as that number is in the directory then a name is displayed. But otherwise it's just a number.
Number forwarding is great. Nice to have a second number for $20/yr to use for stuff like craigslist ads where you don't want to use your real number. MJ has vanity numbers that you pay extra for; my randomly assigned one is full of consonants, ones and zeroes so I can't make it spell anything cool.