You can call and send SMS messages from Belgium to all countries.
For an overview of countries and prices, please visit https://undo.be/tariffs/roaming.
Do not forget to add the prefix of the country of your correspondent preceded by the sign + or 00 and without the first 0 of the number. 

For example: you want to call the number 0402811215 in the Netherlands. You must dial +31402811215 or 0031402811215.