Can't get him to come!

[dolphindreamer28]

I have a 3 year old mutt named Sam, and when he was a few months old we signed him up for obedience, and he passed. He knows the command come, and he knows what hes supposed to do. But whenever I call him, he is so stubborn and he only comes when he feels like it, so I can stand there and call him for like 5 minutes and just sit there and stare at me or run away. I don't know what to do!