I signed up with them because I needed to retain a phone number previously held by another carrier. I had nothing but trouble with them, starting with the fact that it took more than a week for the device to arrive, yet you have only 30 days before you can no longer return it. I did not need a new number; I need to port an existing number. Turned out, despite the Magic Jack website "test" saying my number could be ported, it couldn't--at least not quickly. Two months later I gave up and tried to return the device. (I had NEVER used it and they knew that.) But was denied. So I'm out the cost of the device, the additional money they demand to try porting a number and the other costs associated with the purchase. By the way, trying to get help from a tech support person is very difficult. They are off-shore somewhere so their English isn't good. The 800 number frequently produces a message saying the number has been canceled. (Don't believe that. Keep trying the number.) I recommend not using these people because if there is ANY issue--the device doesn't work, you can't port a number, etc.--there will be NO HELP and if the problem persists longer than the 30 days, they won't refund any of your money.
Recommendation: DO NOT SIGN UP WITH THESE PEOPLE