How do I get legal custody status changed from sole to joint?

States do cooperate with each other in such matters, so it is possible for you to work with the authorities in Idaho, who will in turn work with their counterparts in Arizona, but as you can imagine, especially in this era of economic crisis and budget cuts, both the people you'll be dealing with in Idaho and their counterparts in Arizona are unlikely to prioritize your case above matters involving parents and children in their own states, so your best bet is to contact a lawyer in Arizona who specializes in family law and pursue the matter there. As for what you say to get the custody order changed, absolutely the most important thing to remember is that any decision has to be in the best interests of the children. Judges, lawyers, commissioners, mediators, counselors--everybody in the system--they've heard it all before. They're not likely to be moved by anything other than a clear demonstration that it would be in the best interests of your four children to modify the custody order.  That's the thing.  The only thing really. It can't be about anything other than how joint custody is going to make things better for the children.  You also need to keep in mind the practical reality of the fact that you live in Idaho while your children and ex-wife live in Arizona. That begs the question of how you and your children are going to be able to physically spend time together and how that's going to be paid for.