If you want to call back home, you'll need to purchase the International Landline Call Pack or top-up credit.
The International Landline Calling Pack gives an allotment of calling minutes to landline numbers in the UK, Germany, Israel, Poland, Switzerland + some other countries. It does not include calling to UK mobile numbers.
Extra top-up credit will let you call UK mobiles at a cost of $0.49USD/min.
However, we find that most customers just use voice apps like Viber, Whatsapp etc to call back to home.