My Mother used Magic Jack and hated it. Too many issues to list here but the main one was dropped calls and the phone would actually ring 4 times (on the caller end) before it rang once on the magic jack end. Also it would go into a mode of ringing once and going directly to voice mail.

I have used Vonage before and had no issues, but now I just do cell phones and a cell phone "card" for the computer.

Best of luck,