It is possible that you will get a cell phone from your host parents, so that they can always reach you and the children. This will then be your work mobile phone. You must check with your host family whether you can also use this mobile phone for private calls and text messages. In general, however, you should refrain from using it for private calls and messages during your working hours.  If you are taking your own mobile phone with you, you should check with your provider about international costs or simply buy a local SIM card.