You hang up to avoid a Belgacom charge, and the computer calls you back, providing you with a stateside dial tone so you can dial as if you were in the United States.
You realized that Belgacom only wants to charge you for unnecessary things. 
mnli hypothesis: You realized that Belgacom only wants to charge you for unnecessary things.  premise: You hang up to avoid a Belgacom charge, and the computer calls you back, providing you with a stateside dial tone so you can dial as if you were in the United States.