Have to admit, a magic jack is a hassle, and granted many people will not either want a home phone, or just prefer cellphones.
However, after living with one for going on over a year, I've found some tips:
-do not use your home pc with 3 users on it to run a magic jack
-do use an external USB hub with it's own power supply, the Magic Jack likes to be fully powered
-do find an old laptop to use and have it as a dedicated phone server so to speak, that makes a world of difference, before dedicating an old laptop to phone duties the magic jack would not ring through, would drop calls, had to be rebooted every morning etc, with an old 40 dollar laptop with external usb hub the magic jack has went whole weeks without needing a reboot.
-if you use an old laptop, be sure to go into msconfig and shut off all of the extraneous programs such as MS Messenger so boot times are cut down to the barest of minimums, when I've rebooted the machine it takes less than 45 seconds to restart the box.
The sound quality also greatly improves with a dedicated box and a new phone with fresh batteries and the savings are significant:
Cable phone service 25 dollars a month x 12=300 dollars x 2 yrs.
Magic Jack 20 dollars, new phone 25 dollars, old laptop 30 dollars, usb hub 5 dollars, power supply *free*, the cost per month is less than 2 dollars, though not every phone system can call into the magic jack, for example hospital phone systems are a crap shoot, but you can call into such a phone system fairly easily.