I had moderate success with call quality on domestic calls within the US. It depended on how good the internet connection was for the day, even though I have high speed internet cable service.
In order to use it for International calling, you have to prepay an amount on the Int'l call part of your account, so I did for $40 and decided to try this on my International 14-day trip to Italy. I stayed at deluxe hotels and paid for their internet services so that I could use the phone as well as check my emails. I could never get a quality connection without it major cutting out parts of the conversation, and it would drop the call every 2-3 minutes. I tried at every hotel I was in to see if it was different. It was not any better. No success.
Then I took a 3 week trip to Lebanon, and stayed at a person's home that had internet. We could never get a connection to hold for more than 1 minute, and the connection was not good enough to understand even one sentence.
The only thing I do like about MagicJack is their voice mail service, because I can set it up for the voice mail to drop right into my email box, so I don't have to physically call the phone and pickup messages. Although I do have to physically call the phone in order to delete those messages. For this reason, I extended it on the 5-yr promotional plan of $59.99. But when I approached their customer service about applying the Int'l unused credit towards this, because of the impossibility of using it, they would not. They just stated it was non-refundable and would not expire.
I don't recommend the purchase of this by anyone, because I don't feel it lives up to it's call connection claims at all. The only reason this works for me is because of how I need the voice mail service they have, and $60 for 5 years of that is a good price to me. But if you need it for the outbound calling (or inbound), it's just not worth the risk of it not working for you, since your connection quality fluctuates based on things beyond your control - your internet connection.