Some Windows Mobile and Windows Phone devices require a domain when enrolling
Posted by Heather Burkett on 18 July 2013 12:33 PM

When enrolling a Windows Mobile 6.1 or 6.5 device or a Windows Phone 7, 7.5 or 7.8 device, the enrollment process will not complete without entering a domain.  Even if your ActiveSync server does not require a domain, the device requires that one is used.  The only time a domain is not required is if the username is a full email address.