Editor's note: This story has been updated to correct that while some Realtor associations and MLSs want all of their members to pay for lockbox services, those members would not be required to use the devices. The subhead of the story as originally published stated that the NAR policy under review prohibits MLSs and associations from requiring the use of lockboxes. The policy only prohibits MLSs and associations from requiring that members pay for lockbox services.    ORLANDO, Fla. -- The National Association of Realtors is considering whether multiple listing services and Realtor associations will be allowed to require that their members pay for some services that are now considered optional, such as lockboxes.At least three MLSs have notified NAR of their desire to require all of thei...