My personal opinion...You say this guy is your ex, so I don't see where he gets off asking you to make calls for him. He is in the position he is in because of his own bad choices, so it's up to him to handle the fallout, not you. Good on ya for recognizing that fact.
Regarding visits, I wouldn't go because, again, he is your ex. My thoughts are that you should take this time to take care of yourself and do what is in your own best interests going forward. He'll survive, and being in a place that doesn't allow smoking (if that is the case) will help him quit for good. After all, he's in there to take control of his life, so maybe he should start doing that.
Have you considered not taking his calls? You deserve some peace and it doesn't sound like you're going to get if if you keep talking to him.