Once again I am of the opposite view point. Please know that my 'critique' is not meant to be hurtful and my intent really is trying to offer you some support.

Your son is not your friend nor should he be. This is a critical time in his own development and you need to be supportive of him and not vice versa. You need to be there for him. I would suggest his not being at your beck and call has everything to do with this. If he resides with you, you have no need to call him unless it is a dire emergency. You should not be dumping upon him. You should recognize he needs his independence. Again, you are a parent and not a friend.