We've used MagicJack at home for about 5 years now and I've had problems come and go. I've worked with the so called tech support through many issues, but it really comes down to the technology. The best thing I ever did was about 3 years ago when I purchased an inexpensive powered USB hub. I learned that the MJ required more power than most on-board USB circuits provided. After adding this $10-15 piece of hardware, my problems pretty much went away with exception of a few hiccups here and there.
I will add, though, that MJ is a bandwidth hog. Unless you have a really solid connection, you're going to hear a lot of distortion or the person you're talking to will.
Since we hit the road fulltime several months ago, I knew that my connection would not be as good as at home so I moved to Skype. I pay Skype $2.99/month for a phone number where anyone can call from a landline or cell phone. This seems to work much better than the MJ with lower bandwidth, which hasn't worked well since we began travelling.
Hopefully some of this information will help you.
You can read my fulltime blog at: http://longlongwaytotipperary.blogspot.com/
I use a Verizon aircard through Millenicom and am very pleased with the coverage. I use this in tandem with a wifi antenna on top of my coach and both feeding through a CradlePoint router which redistributes the signal in our coach. It's a great system and pretty inexpensive to get going.
I have more details about it on my blog if you'd like to read it: http://longlongwaytotipperary.blogspot.com/p/technology.html