I have magicjack and I have noticed that when it starts breaking up there are a few things that could cause this:

1) If you have too many programs up on your computer\

2) If your internet is slowing down

3) check the usb on the magicjack and see if it is loose and you may have to order another one. If you do they will make you put a deposit of $40 and when you send your old one back they will refund it.

4) Also go to:

Start> Run > Type: msconfig > Click on Startup > Uncheck all > Only click on items starting with I's & O's

5) Download the update: http://www.magicjack.com/1/magicfix.asp
Click on the orange box

Hope it helps~~!!