How to populate Simple Display Name -field to all mailboxes and what if it's empty

Hi

We want to use Simple Display Names with external emails. How to populate SDN -field of all mailboxes same time. SDN should involve information like "Firstname Lastname"

And what happens if someones SDN-field is empty when using SDN?

We have Exchange 2010SP1 and Windows 2008 R2

~ Jukka ~