When i got my first magic jack, the big question i had was how is the sound quality. From an expert who has been using magic jack for quite some time now i am proud to say absolutely amazing.
The one thing i noticed with the magic jack is if you are going to be downloading heavily, using up your bandwidth, you may experience choppy sound quality. This is not the fault of the magic jack, instead that of your bandwidth by your Internet service provider. I have an office VOIP system by another company as well and when we are using the bandwidth heavily that phone chops out as well. A simple fix is to stop your downloads and resume when your call is complete.
I put this to the test to ask many people when calling them if they could tell i was using a magic jack and they all said no. The only ones that could tell were those that i called while heavily using my download bandwidth.