Gall stones that leave the gallbladder should pass into the stomach. But sometimes the stone becomes wedged in the bile duct instead. These are referred to as bile stones. This happened with my uncle and apparently, it was quite a large stone. He was in a lot of pain and it was considered a serious condition, resulting in him having surgery to remove the stone. This was some time ago and required a large incision.
I believe they can do Shock Wave Lithotripsy now, which is similar to the treatment for kidney stones or Mechanical Endoscopic Lithotripsy. Neither are invasive like open surgery.