You can successfully complete all the steps to set up a corporate exchange account on a mobile phone but when you click done it's stuck on the "Loading" screen with a wheel.  We had this problem and managed to fix it. We recently upgraded to Exchange 2013 and had problems migrating a few mailboxes. The same problem mailboxes were stuck on loading on ActiveSync on phones regardless of the make or model. To fix I went to properties of their AD account, Security tab(Must do View>Advanced Features to get this) Advanced and check Allow inheritable permissions from.... check box and hit apply. Removed ActiveSync account from the phone and started again and mail worked immediately.