Can you fill us in on a few details? Sometimes their specific drug of choice is important -- meth for instance makes an addict very aggressive, so you have to be careful about that.
Does he have a history of being physically OR emotionally abusive?
Do you feel safe?
Is he threatening you on the voicemails?
Have you answered him at all?
How old are your children? Is he a good dad and 'devoted' to his kids?