If your contacts use different File As formats and you’d rather have all contact use a single format but changing each contact will take too long, you can use VBA to change the File As format on all contacts within minutes.

Code sample which was tested with Outlook 2002, 2003 and 2007 is available at
http://www.slipstick.com/contacts/file-as.htm#vba
It only works on contacts in your default Contacts folder.