I don't have the newer Magic Jack but I do have two of the original with plenty years of service left on them. The Pros to Magic Jack is the fact for very little money you have a spare phone number and voice mail. The con is nobody can hear you. If you actually answer the Magic Jack call you can hear the person talking but they can not hear you, and if you call out it is the same. For the original model you do need internet and it plugs into your PC. I love my Magic Jacks for the voice mail it provides. I do not have an actual landline anymore but for calls I use my cell phone.
On an unrated note I found Magic and Jack the founders little girl's two Yorkie's cute.
I have heard about it, thought about getting it, etc. However, I decided to try Ooma instead because I know someone who has it. I bought mine through Buy.com in the FusionCash mall. It arrived yesterday. I am still waiting for the cash back to post to my account.
I've stress tested it. It is hooked up to my cable modem and sends the internet signal to my router- though I could put my router first. I called a cell phone and a land line (though not at the same time) while running two netflix movies and surfing the net to see if the call quality would go down. No dropped calls, cutting out, breaking up, etc. I guess my voice sounded a little "tinny" to the people on the other end, but they sounded normal to me. It is still VOIP.
The cons: you have to pay for the Ooma device up front.
The pros: you only pay a few $ per month for service (about $3.70 where I live), get tons of features for free (including long distance and voicemail), can choose your phone number or port your existing phone number, and you don't have to have it connected to a computer.