Hello,
To find all users with the Dial-In property set to Allow, you can either perform a directory search using LDAP filter
(&(objectCategory=person)(msNPAllowDialin=TRUE)):

or you can create a Business Unit that will include all users with the msNPAllowDialin property set to TRUE, using the very same LDAP filter:
(&(objectCategory=person)(msNPAllowDialin=TRUE))
