I've used my magicjack all over Greece, as well as Mexico, Central, and South America with good results. Results are dependent on having a reliable internet connection.
Faxes don't work well with MJ. Some people have gotten it to work, but it is reportedly not terribly reliable.
Here is a post from elsewhere:
Originally Posted by LVTrave
Magic Jack has an extensive FAQ on their website.
http://www.magicjack.com/2/faq/
Part is here:
Your Question
Can I send and receive faxes using magicJack?
Answer
SOMETIMES.
We do not officially support using faxing with magicJack.
Please try the following steps to use magicJack with your fax (contact your
fax manufacturer for details):
Turn off error correction on your fax machine or program
Set the fax machine or program to use the slowest speed available
Increase the speed, checking at each speed that faxes work